Turn signal trouble shooting

I don't know where all you measured those voltages you posted, AKA are they at the rear lights, or at the left kick panel connector for the rear harness, or up at the TS connector.

I would start either at the TS connector or the left kick panel connector. Find those connectors on you shop manual draw them out and note the colors and function. Then measure them out. You can also check for brake light power there. With the turn lever centered, brake power should go to both rears. And you can check the LF and RF there as well. Depending on what you come up with, move to the rear. It almost sounds like a rear socket grounding problem. Do not negate a wrong bulb, defective bulb, or bulb jammed in a socket 1/2 turn off which can happen if the socket is rusted/ abused, or the lamp bayonet is not "sticky outey" very far