OK - identified the three contact points on the board for the phono input "module". The connections are not wires, but extensions of the module RCA contacts (as are all of the RCA jacks on this unit).
On magnified inspection, solder joints appear to be solid. I did a little scraping between connection points to remove what appeared to be flux between them. I'm wondering if my next step would be to de-solder the three (L, R & Com. Grnd.) and try to remove the module for a visual inspection and continuity check. My guess is that the contacts inside the RCA jack module have worn or spread, and I doubt that I can access them within the module to close them up. Your thoughts on any of this, and do you know if replacements are available for these?