||My guess without looking at it would be it's delamination. It was common in the 85 thru 92 units in the industry. They used petroleum based glues back then that when assembled would eat the styrofoam insulation. It would be like taking gasoline and pouring it into a styrofoam cup. It was called a 4 piece Eastern sidewall. They now make a 5 piece Western sidewalls. The extra layer is a luan board that is porous enough to absorb the glues. Also since 1994 the EPA changed the glues that were allowed to be used and they are now more foam friendly. What would happen is the manufacter would spread glue on the framing and then when the wall was sandwiched together the glue would squirt out onto the foam cavities and eat the foam up. There's more to it then that, in fact, I had to use 2 pages in an article I wrote on it., but that's what you have. Once it starts to delaminate then the weather takes over and start to pulp the sidewalls out. If you have pulping, stay away from it.