I got very little help in the past with this either.
I do know there is some 'plastic' (whether it be acrylic or not I don't know) in the composition of the body. Bakelite chips easily as doesn't warp so I ruled that out.
The issue though is the lunettes, which definitely contain formaldehyde, and the cellulose lacquer applied across the plaques.
It appears that when the cellulose deteriorates (the vinegar smell) to the point where air gets to the formaldehyde, then the formaldehyde leaks into other areas and causes the damage. I think the vapor itself causes damage, hence anything else located close to the affected plaque can be affected.
I've had some success with application of car lacquer across the plaques, although I suspect this only slows down or at best stalls the deterioration, and it doesn't work if they are too far gone.
I'd always assumed the storage (temp & humidity) was a big factor in this, but like you I've found perfect and really bad items within the same lot before.