Hey guys,
My right rear brake is getting pretty hot.
I had my '68 145 parked for the last year while traveling and after a short test drive I began to smell hot brakes, the right rear was the culprit and after inspecting the caliper i found that the recently replaced outer pad had more wear than the inside, the outer piston seal had cracked and the piston seized.
i have just installed a fresh remanufactured caliper and found that while bleeding the system it was pretty hard to push the pedal with the RR bleed valve wide open.
The brake is still dragging heavily and overheats with a minute or two of highway speeds.
Is my proportioning valve likely to blame or is there something else in the system that could be blocking the flow to and from that caliper?

my MC is an ATE and is new.
flex hoses are maybe 4 years old
system is bled every year
I have never serviced the aging proportioning(?) valves.
pads and rotors are all near new.

As assume its the secondary circuit valve is there anything i can try on the bench top to help? a cleaning? is a rebuild kit required or even available?
Thanks, Andrew