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?