To many people "leather" is just leather, but it's not, modern leather [post 70's in most cars, post mid 90's in Rolls and Bentleys] is very different today, it's thinner for a start, therefore softer and it wears more quickly, it's not inferior, it just needs more care.
Why? Well when leather is tanned, moisturising oils are impregnated into the hide, with older "thick" leathers this stayed within the leather for many months before heat evaporated it, because the new leathers are thinner, the moisturizing oils dry out more quickly. Now that cars must be completely locked up for security reasons, a hot day with an outside temperature of 70 will convert to over 100 degrees within a locked car, baking the interior.

The seat design can also determine the rate of "wear". Bucket seats which grip the body, crease less, however they wear more quickly on the bolster cushions because in many cases the only way in or out is to rub this area up or down when trying to get in the car, big broad seats as in Rolls-Royce and Bentleys, crease more, whether the person has a big or small bum, a little bum has more weight on a smaller area, causing creasing in the central area, a big bum causes creasing over the whole cushion because of the associated increase in weight.

How does one preserve the leather now that it's thinner, baked in sunlight for part of the year, frozen and then blasted with air conditioning for the remaining months?

Firstly keep it clean, if you look at a mechanics fingers you will note that the skin is dry and cracked, the cracks have ingrained dirt in them which is effectively holding the cracks apart, this is what happens to your leather if you neglect it, so wipe it down with a damp cloth every month, clean it thoroughly every 6 months but not with soapy water or a chemical smelling watery cleaner, leather when wet expands, on drying it shrinks, look at what happens to a chamois leather, the more leather shrinks the more it pulls on the stitching. Use a thick mild gentle cleaner, neat for dirty leather, diluted with a little water for regular cleaning, the best has glycerine added. Next, one has to replenish the oils that were originally put in at the tannery, but with which brand?

Never use "oils", these will rise to the surface in hot weather, transferring to your clothing, look at the instructions on the bottles of creams or pastes, if they say, "polish off" or "buff up" after several minutes or hours, avoid them, why are they telling you to polish it off? Simply because it hasn't soaked in. These also leave a residue on the surface which attracts dirt, they can also become sticky in hot weather. To work effectively it must soak in immediately, others say that applying in warm conditions speeds up effectiveness, rubbish, they do not work. Equestrian products must not be used on auto leather. There is one brand which wins all the Auto magazine comparison tests, it even smells of the traditional English leather that was used in hand built cars.

Leather, the need to restore.

The main problem with expensive sports and luxury cars is that the first couple of owners are so rich they are not bothered about looking after the car's interior themselves, it's only when an enthusiast who has always dreamed of being able to afford his dream car, buys one, he or she wants it to look it's best, to restore parts of the car that have been neglected. The leather is the main area to have lost it's original finish, creases, cracks, colour rubbed off and ingrained dirt, cleaning and conditioning as above will greatly enhance the appearance, small touch up leather dye kits are available to colour in cracks, creases and scratches, these greatly improve the appearance without the trouble and expense of total re-colouring of the interior.

The car needs restoring with lots of general work on it and it will take months.

Many car enthusiasts buy a car and think it will be restored within a few months, most are wrong, months changes to years and they ALL make the same mistake of leaving the leather till last.
First mistake. Leaving the leather in the car, dust, overspray and damp attack it.
Second mistake. Taking the leather out and storing it in the loft, where one minute it's cold and damp, next warm and dry from heat rising through the ceiling.

Third mistake. Covering it with polythene or just news papers.

What one should do is remove the leather trim from the car and give it a thorough clean and conditioning with a conditioner that soaks well in immediately without leaving a greasy sticky finish, never pile it on expecting it to soak in over the following months. Then store in a cool dry room covered with white cotton sheets, if the room is subject to dust, cover the sheets with newspaper, which are replaced periodically, then when your car is ready to accept the trim it will still be in a serviceable condition, rather than dry, brittle and infested with moths.

Re-colouring kits/systems, why the traditional way is wrong.

Re-Connollising is a well known system for adding a new layer of colour to leather seating, a system developed by Connolly Brothers that has for years been the traditional method of "re-dyeing" leather trim.
The kit consisted of an Ammonia based cleaner, a cellulose based "dye" and a "Hide Food" paste, later kits used a water based dye with sealant.

Lets look at what leather trim is and how it is effected by chemicals, liken it to your own skin.

Ammonia when applied to your hands strips out all your natural skin oils your skin turns white, it's dry, stiff and lifeless, then apply cellulose paint, its then even dryer, when dry try using the wife's hand cream to repair the damage to your dry skin, result- nothing.
Next consider the stitching, a cotton and nylon mix [dependant on age], nylon is attacked by spirit based dyes, they melt it.
So the system was;
1. Clean it with an ammonia based cleaner that stripped out the oils, made the leather shrink and go hard.
2. Spray/paint it with cellulose paint which weakened the stitching.
3. Apply "Hide Food" which was prevented from softening the leather by the layers of cellulose paint.

Result; after a few months use, the seats cracked again.

Re-colouring. The common sense approach.

For best results remove the seats from the vehicle.

Thoroughly clean the leather with a thick soapy solution which contains glycerine using a soft finger nail brush to remove all the ingrained dirt, wipe off , repeat until clean, immediately apply conditioner sparingly to soften the leather further [the glycerine in the cleaner started the process], apply further applications of conditioner until the leather is very soft.
Clean again lightly with the original cleaner, wipe off residue and leave to thoroughly dry. When dry "degrease" the leather all over paying attention to in and around the seams and stitching.
Apply the water based dye to the leather, the first coat needs to be applied by hand and rubbed into the areas which have the most wear first, then all over, this will form a good key for the main coats which can be applied by sponge, brush or mini roller, however nothing can beat spraying which is the most economical on dye and gives the best finish.
There is no need to apply conditioner for many months because like when new the leather was impregnated with moisturizing oils first which will remain in the leather.
This system will give you a finish that not only looks natural but will also last for many years.

How to look after leather upholstery. I will split the world into 2 halves, North and South because heat is the most destructive problem. If Dye transfer from clothing is a problem it can be removed with a product from Gliptone Northern countries. If the car is used daily, once a month wipe over the seats with a damp cloth, every 3 months treat the front two seats with conditioner, twice a year the rear seats and other trim panels. Once a year clean thoroughly with cleaner, during a hot summer treat the driver's seat with conditioner every 4 weeks. If the car is rarely used, halve the above recommendations. Southern Hot climates. Treat the leather twice as often as above. Apply conditioner sparingly

Gliptone Leathercare Ltd, 2006.
01706 819365. www.liquidleather.com