In my opinion, you can spend a lot of time, and money, and even after it is repaired, the 1992 Monterey may still be only worth $1200.
I believe the only way that you can properly repair delamination is to completely remove the side wall, take it apart, replace all damaged wood and insulation foam, apply a better adhesive, and then put it all back together again using compression to hold the sidewall flat while the adhesive sets up.
To me this is not s DIY project and should only be attempted in a factory type environment. Even then, the time and materials involved would NOT increase the value of the coach being repaired. Of course, there is probably interior ceiling panels that also have to be dealt with as well as rotted floors from the leaks.
Stopping a roof leak is pretty simple basic repair work. Dealing with the delamination and other damage that has already taken place is the huge problem.
I would find another project Class A without delamination issues.