Tell me any brand and any model amp that has not had output transistors fail. OK, among amps that HAVE transistors.
When output transistors fail, you generally have blowing fuses.
Start at the start, verify the power supplies are up to voltage and clean. Make sure none are missing from the circuits. Frankly as transistors go, I;d probably be more concerned over drivers from your description. Open resistors too. Cracked traces or solder is a common problem in any amp.
Most bad parts don't look a darn bit different from good ones.