The thermal compound is old and used by now for over a decade. I would take some isopropyl alcohol and some Qtips to really get that stuff out of the way. It is important that this compound fill in the cracks that may exist between the heat sink and the chassis. Fresh grease is way better and more reliable. The last thing we want here is for the output transistors to overheat.
Keep up the good work and let us know if the soldering makes any difference on the amp. Good luck.
Keep up the good work and let us know if the soldering makes any difference on the amp. Good luck.