Picked up a KR-4200 in nice shape. Had to replace the stereo light, tuner indicator light, and did a general cleaning. Used Deoxit on all switches and pots followed by electronics cleaner. Speakers play well on A and B settings. However, when I switch to A+B, B speakers are fine, but A speakers are super weak. I did go back in and take a close look at that switch and saw black dirt/oxidation on the contacts. Did a combination of mechanical and Deoxit cleaning, but I still have the same issue. Not sure how I am going to get in there to clean better without disassembling the switch, which seems a bit daunting. Any advice? Is this pretty clearly a dirty switch? Thanks!