I don't have time to read the entire thread so if my advice has been covered just ignore me but I will say this is why you need thoroughly bench test an amplifier after you repair it. I'm not talking about just powering it up, I'm talking about hooking it up with a dummy (resistor) load and feeding it a sine wave for 12 hours. I own Perry Babin's repair tutorial (the creator of bcae1.com) and that's one of the big things he stresses is proper testing after you believe it's fixed.
As a side note, I have some awesome gigantic resistors for load testing. The company I worked for was cleaning house and they were just going to pitch em but I saved them. They're like 12" long and 2-3" in diameter, capable of handling hundreds of watts. But even running the amp with a few 50w resistors at low power would be better than nothing. You could also use a speaker but that creates a lot of noise and if anything fails in the amplifier you have the potential of damaging the speaker.
Also I'm not trying to lay into you or anything, I think your taking the proper steps to make it right so no reason for that //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif