Thanks to those who replied.
1) there are no trailer wires
2) all grounds are good, re-done, new etc. So not a ground problem
3) flasher itself (both turn and hazard) are working normally so not the flasher
4) i actually re-wired (temporarily) the RIGHT lights to the LEFT lights (in parallel) and everything works...further confirming it's not something ike a light bulb or a bad ground at the bulb socket.
The above post gives me a real (not a guess) lead -- I now suspect the trouble is in the turn signal switch itself - with the lever in neutral, both rear lights SHOULD be connected to the output of the brake light switch. But one is not lighting...maybe the turn signal switch on the steering column is faulty. It would also explain why, when using either right or left TURN (when the switch is in turn mode, not neutral positiong) that the rear lights each blink properly, ie, the wiring and the bulb and the socket are all functioning NORMALLY...also, no fuses are blowing so there is not a short anywhere. Remembering that the Blink and Brake are on the SAME circuit. So...somehow the TURN position is working but the BRAKE position (right side) is NOT.
I bet a dozen donuts it's a faulty turn signal switch. This is the best thing to go on, thus far, i mean, logically this makes perfect sense and the reason why I found no probems in the rear-end wiring after hunting for 2 to 3 hours the other day. No problem to be found back there.... Any other thoughts?