So it turns out that my recapped Sansui AU-417 had distortion in the right channel. I contacted the seller, and he had me try Deoxit (and I also did a DC offset check), but no joy. So, he had me send it back to him (it turns out that he does the recapping & glue cleanup himself as a hobby - his feedback is full of various AU-x17 amps).
He received it and he reports that it was a broken solder joint. When he re-soldered the joint, the distortion went away. He readjusted the DC offset and bias and has shipped it back to me.
So, the morale(s):
* If you are looking to fix an audio problem in vintage electronics, be sure to look for bad or broken solder joints.
* Shipping of old gear is liable to shake something loose.
And it is cool that the guy wanted to stand behind his work...
Does it break any forum rules to list the seller's name? I think that in the world of vintage electronics it's nice to know that someone on "The Bay" operates like that. I'd surely buy something from him rather than another seller knowing how he treated you.
Okay, I received it back, and tested it with headphones and speakers, and now it is clear and crisp. So, here is the link to the guy on ebay:
BTW, comparing the fixed and recapped Sansui AU-417 to the aged Kenwood M2A:
The AU-417 has a hair more clarity, while the M2A has more bass and dynamics. The former may be due to the recap, while the latter may be due to the significantly higher power reserve.
The M2A has really excellent "PRaT" (Pace, Rhythm and Timing), it really gets your toe tapping.
While I did test the AU-417 with speakers, I have not yet done so with the M2A, because I am still trying to figure out the weird speaker connections on the back. When you turn them all the way, they only lift up enough for a relatively slender wire...