Should I change out these output transistors out on this 1280 that I am trying to freshen up? They test good but as you can see in the pictures they have small burn spots with what looks like copper showing. What could have caused this and where should I check for other issues that may have? Is there a source other than Ebay to find replacements for them and for the clear insulating pads? Or, can the insulating pads be fabricated somehow? Thanks!