is buying used Mcintosh equipment online bad idea?

was trying to build system like my college buddies had 35 years ago, and bought a MA-6200 that has static in one channel that the local dealer cannot isolate now. Fixed it once, but one loud listening session, and it started humming loudly, and the speaker overload lights came on. Turned it off and when I tried it again, the static was back in same channel but worse.

Tried to buy a used 2100 and bypass the power amp, but regardless of gain settings, the sound is distorted at anything above talking level volume with this amp. Changed out audio source, preamp, cables, speaker wires, and distortion remains. Returning it for refund. Have I done anything wrong in setting this up?

Live <2 hours from Austin, and may try taking the MA-6200 in to a vintage stereo shop there. I run a pair of Klipsch original Heresy that were late model, but are over 25 years old. Not a lot of heavy use on them, and have not tried swapping them out.

Is all this old McIntosh equipment probably in need of having a full test and update before buying them, or at least a listen to them? Just found this website, so I did not buy this stuff here.