I wouldn't push hard on lettering's inks or paint. That part should really be addressed on a car by car (& brand,age) basis. Too many variables. Water alone can remove some train paint.
Forgot the issue was a lock on until I was done lol.... read on if you like... Im gonna try it on one for you. (I don't care about the ink) And will tell you later.
Note sheeted paint that covers large areas is often more stable than lettering etc. Edges can be a weak point too. Some cleaners, oils etc can creep under the edge and lift, even though the paint remains solid.
I'm not aware of vinegar discoloring plastic, that's all I got other than Grandma cleaned about everything with it. (try it with newspaper as a wipe cloth on a window and you might give up on Windex.)
There is no magic "clean-all", everything has an exception. So test, consider, decide.
Lionel used to suggest Naptha (zippo fluid) for plastic (with notes about paint, just like us) Gramps used it on all his Lionels (about 50ft of shelves worth of display, + junkers)
