Thanks for all the suggestions. I should have been more specific. The filth is not so much on the circuit boards but mainly behind and in the hard-to-get-to corners of the amp casing. I can see it with a flashlight but I can only barely touch it with an elongated Q tip. I suspect this poor amp was stored in the basement for years because the owner didn't want to deal with fixing the left channel circuit board issue. If you press down on the circuit board, the left channel pops into place. Let go and the channel goes out. Otherwise the amplifier sounds nice in spite of the filth and even oxidation on some of the circuit board components. This amp even had an old dust encrusted spider web complete with dead spider. Disgusting!!!
Audio Repair Tools
I have a Spectral DMA 200 that needs to be dismantled and cleaned as it is FILTHY inside. It also has a circuit board connection issue. I have the hex allen wrenches needed to take the screws out, but I don't know where to find electronics tools that are thin/small and versatile enough to properly disassemble and reassemble the internal components. I couldn't find anything on eBay. Does anyone know where audio repair guys and do-it-yourselfers get their tools???