Dear @mlaughlinnyc,
What I have found over the years is these types of stains are caused by the car lying on its side against a surface that at some point either got wet and/or was in a humid environment for extended period of time.
The only product which I have used and swear by is "John's Restorzit" that was available at York by a TCA member. That product works magic on tin platted products. It will restore that finish to like new and clean away the marks and stains you see on your cars.
Unfortunately this product is either no longer available or the nephew of the man who developed it hasn't attended a TCA York meet in sometime.
There have been many threads on this subject. If we could locate this individual then he could maybe make a batch for sale.
The only issue is, it cannot be shipped. It would have to be picked up in person.
