I brushed on few coats of glycerine thinned with water on the hard dirty seats it soaked in I plan to give it more coats. Don't know if it will help but I don't think it can hurt. It does soften leather I have been brushing it on end caps and soaking door check straps and its helping. It is loosening up the bird crap.
Interesting, the Smithsonian uses a similar mix with others added for various leather artifacts. I guess a bad outcome would be a stretchy gooey mess, but we shall see.
SMITHSONIAN GLYCERIN TREATMENT
59 percent glycerin (glycerol)
39 percent water
1 percent formaldehyde or 1% Dowicide (TM) 1
25 percent glycerin
75 percent alcohol
Artificial leather is not leather. The upholstery on your '16 for all practical purposes is cotton oil cloth. Linseed oil was most likely used in the creation of the finish.
In my opinion based on my own experience, the best thing to do is clean it with mild soap and water to remove the dirt and then leave it alone.
Don't coat it with anything. Hopefully, that glycerin has not gotten into the cotton backing.
I suggest washing off the glycerin.
You are very lucky to have such a nice, unrestored car with very good upholstery. Just accept that the old leatherette is what it is. Get rid of the dirt. There's nothing you can do to soften the finish.
As far as softening the bird crap - soap and water will remove bird crap.
thanks Ed and Eric I have thought this out and I think it is the best chance to save the seats the car was in a small garage with no ventalation for many years very hot in summer on some spots I can break the fabric by pushing on it. while I have more work to do to make car relible it is running very well the back tires are on. when I get the fronts on it will be ready for a short ride my 97 year old uncle is going to show me how to drive it! I am trying very hard to keep it original but I think the first butt on seat will break it apart.Glycerin is the same stuff used in cosmetics and medicen I will keep you posted how it works
Glycerin is a simple alcohol so it may help to soften the lacquer coating. The problem is the 99 year old cotton backing which is more than likely being held together by the coating.
Unless you plan on having sex with the cushions, I wouldn't put glycerin on the upholstery.
Just clean it with soap and water.
Two things can happen with old leatherette (oil cloth).
The surface gets hard/plasticized and cracks. It can also de-laminate from the cotton fabric. There is nothing that can be done to reverse this.
The cotton fabric itself can be rotten and be prone to tearing Again, nothing can be done about this.
Just accept it for what it is and live with it.
I apologize for preaching.