Hi Craig.
Are there the standard Rover 200/400 rear claipers? If so, I know the Rover guys have quite a few problems with them seizing/sticking the same as you.
Only thing I can suggest is try a new set of calipers (possibly recon ones) or recon yours.
Theres a really good tutorial here:
http://www.rovertech.net/forum/viewt...hp?f=6&t=50092
If you can't read it or not a member, I can try and paste the contects here.