Leather could still need some regular conditioning when required.
All surfaces can get dirty. That includes leather.
For cleaning, use saddle soap.
There ARE specialist protectants for leather, but their aim is to keep it supple, flexible and to a certain extent, elastic. The elasticity is especially needed in the vertical seat bolsters either side of the driver' back. It is in this area that leather in particular can show ugly signs of failure, which require expensive repair.
The best place to look for a good quality leather conditioner is in an upholstery shop, or a business that sells domestic lounge suites.
The best way to prevent gassing out of products such as leather conditioners, is to cover the seats with seat covers. If you wish to present your vehicle for concours judging, then temporarily remove the seat covers.
My car has partchment (bone coloured) leather upholstery. When I first acquired it 14 years ago, I spent quite some time cleaning the leather with saddle soap, let that dry very well to prevent fungal degradation, then treated it with a specialist leather conditioner, then covered the seats with cream coloured sheep skin seat covers. My car is not of concours standard, and so the sheepskin covers remain in place.
I treat the leather in my car perhaps at intervals of four years; it is only driven on average about 2,000 kilometers per year, and is always garaged 100% of the time between outings. This treatment should be repeated perhaps once a year, if your car is driven much more regularly, and often spends extensive lengths of time un garaged.
