Some more musings:
I was rather hoping the -12V rail was the problem, because you just seem to have too many unrelated faults.
What I'm now thinking is that at some time it was powered up with those plugs in the wrong way round, which probably put all sorts of voltages in totally the wrong places. This would account for the cooked resistor, the (possibly) faulty 13700, and the lack of waveshaping or envelopes. The amps all use the + and - supplies and if these got reversed anything could have happened.
If it looks like this is the case, you will need to decide whether for curiosity's sake you want to work through finding each faulty part, or just do a chip 'blitz' and replace the lot. The latter is an attractive option as all the chips are plugged and (apart from the 3080) all are still currently available.
If I was doing this for a customer, the blitz approach is what I'd use (it would actually be cheaper for them as far less time would be involved), but being an ornery type, if I was doing it for myself I'd want to know exactly what had gone wrong
It wasn't me!
(Well, actually, it probably was)