Wtf!

A leak causing a difference between LF and RF calipers sounds unlikely since both are on the same plumbing. A leak would take out both sides.

If RF is truly not working, most likely due to a line being plugged with rust. I had trouble bleeding the RF caliper in an Aries once and had a helper push the pedal with both feet with engine running (vacuum boost) and a slug of rusty metal finally shot out. I have used silicone DOT 5 fluid in all my non-ABS cars since. If you jack that wheel up, you can see if the brake does anything. Another possibility is that the LF pad is grabbing, due to impurities like oil or brake fluid. That can happen in drum brakes, due to their greater sensitivity to coefficient of friction (self-jamming effect), but doubt calipers are as touchy.