Any time I had only one brake that would lock it was because there was some type of blockage going to the opposite brake causing too much fluid going to what is the good brake that locks up. It sounds like the line from master cylinder to rear is fine and it's probably the block or line to the right rear brake.
Good thought. It generally is the weak brake that is the problem but I don't think so in this case.
I've removed the "tees" from the system to ensure they were clean. I also blew out the metal lines prior to putting everything back together. Remember, this is a single pot master cylinder so it only has one line that feeds all four corners.
