The procedure for separating the PSU from the chassis is 3 freaking pages long. So I decided that I was not that ambitious and for the time being not to re-cap the PSU but the capacitors are on order. Sometime in future when I'm bored I'll get around to it. In the meantime I checked all the supply voltages via this handy pictorial out of the manual and they are all in spec. The HV measured -1857V vs -1900V which is close enough and didn't fiddle with it.

This is the attenuator section with channel 1 on the left and channel 2 on the right. It uses the same gold leaf contacts found on other Tek scopes. Cleaned each contact with a dab of deoxit followed by a rinse of 100% IPA then blow dry. Any other noisy controls cleaned. The defect the seller noted on channel 1 was simply due to a dirty DC - GND - AC coupling switch.

Left to do is calibration/compensation check. I should have that done later today then it will go for burn-in.