Thank you all for your info and suggestions. My '59 Buick is a promo model, I think, or maybe a toy. It had a friction motor that is missing, which is OK because I just wanted it for display. I got it for a quarter of the price of new/old models or other promo models. I am re-creating my favorite real cars from the past. It appears that my 'glass' has yellowed from age. There is no clearer area where it was attached to the body but yellowed uniformly throughout the 'glass'. I will try the alcohol dunk and check out the window 'glass' at Modelhaus.