My understanding is that there are two types of degredation that can aflict our models.
The less serious of the two is paint rash which as the name suggests is when the paint itself degrades to form, well, a rash. This can sometimes be sanded out and the affected part(s) repainted.
The other is a pox where the models metal body begins to break down making the metal unstable and lifts paint.
From what I have read the metal at some point in the early stages of mixing its various ingredients together becomes contaminated by impurities in the mix.
In extreme cases, eventually they all become extreme cases, some parts can become so brittle that even light handeling a model can cause parts to break off, pillars to snap, hood and trunk lid hinges to break off as though they were soft cheese. There is no remedy for this problem, no retarting its advance - nothing. And there is apparently no indication
when new that a model will start to crumble. Escentially, a model affected in this way has become only junk. I have two pox ridden models - both from Danbury Mint. A 1951 Ford Victoria HT & a 1940 Ford deluxe Coupe.
Both models were bought that way and at very little money because of this. I needed both for parts and one, the 40 Ford, for a project that will end up as a rough as goats knees well used dirt track race car from, Warren, Ohio.
But it would be as dissapointing as all heck to have bought either of these models when as new releases they started to fall apart sometime after I got them home.