I have a CT-17 that I bought new back in 1990. It has occasionally had the same problem with a right or left channel dropping. The problem is likely oxidation of the pins/sockets on one or more of the several small cable connectors in the front right of the unit just inboard of the volume control knob. As far as the inputs other than the AUX, I have had excellent service from Roland at Hi Tech Audio repair out in Oregon. I'd bet he could refurbish it--pricing is on his website. The CT-17 is quite complicated/compact inside and I think I'd let an expert help. I don't have experience with the C-1 or C-11 so I don't have any basis for comparison, but FWIW, I really like the sound of my CT-17 paired with my M500t. I'm currently in the process of upgrading the M500t to the MkII configuration.