I have grown to dislike the word patina. In my mind it was always the green verdigris color found
on ancient bronzes in the museum. Now it seems its normal use in the
toy train world is to describe the rust, dirt, etc on the marx caboose
Flea Market Freddy found over the weekend and now has on ebay for $50
plus $19.80 shipping.
I do agree with Jim, gentle cleaning or no cleaning. That lettering is very
fragile.
Good Luck