Unequal shereo channel output ?

Good question re: all the inputs? If all ARE involved- Find some interstation noise on the tuner, switch the MX to "MONO" and if the output is still uneven: switch the L & R inputs to the amp as Timrhu suggested. If the channel with the lower volume doesn't swap: You know it's the 2205. At least you can narrow it down that much.

Given your 2205 contains some 45 transistors, 49 diodes/rectifiers and 8 integrated circuits: It would behoove you to find a qualified McIntosh service center, with the diagnostic equipment, documentation and familiarity to correctly repair the unit. Once you have convinced yourself that the amp is the problem that is. (http://mcintoshlabs.com/owners/mcintosh-service-network.asp)

Any piece of gear that is still cranking out music after thirty-something years will require service and $$, regardless of where it was purchased. Hopefully- It'll last you another thirty, should you continue to enjoy it that long. Happy listening!