Hello,
Before I buttoned everything up for the work week, I put things back together and gave her a test run. Some success, some remaining issues.
---Receives FM and AM signals. the FM stereo red light even came on for a split second on one channel!
---Definitely sounds better all around from the cleaning. The crackling and popping has gone away.
--- The issue now
(or still, rather) seems R/L channel related. Both channels work, to some degree. The L channel is strongest, and at times is absolutely loud, clear and impressive, for 60 years old. In order to get the R channel to work at some "reasonable" level, I need to find a sweet spot in the balance. It's not as simple as moving balance from R to L or L to R, at times the signal seems to jump in strength for one side, or the other. When isolated, the L side can really boom. The R side is always the weak link. If they are both working together at similar output, its ok, but clearly a weakened quieter output from both. I do think all 8 speakers do work.
I think........
So, I now understood the two channel concept, and how it is in the DNA of the whole system. I am going to keep working to learn new stuff. Watching tons of YouTube videos about basic electronics, audio electronics, ohms law, etc. Ordered a book on the subject, yet to arrive. I'll keep the knowledge journey going forward. It will be a long long time before I will be ready to test various components or replace them. But I do think I can do it, just down the road, once I'm "smarter"

. I'm still in no rush to do anything I don't know how to do. To keep some progress going while I learn stuff, I'm going to look at ordering some replacement parts for the record changer. Seems with some sleuthing that's within my wheelhouse.
Onward and upward!
Matt