This is difficult for me to answer without inspecting the caliper. Did the piston move in and out freely after you cleaned it up and replaced the seal? Was the caliper or piston rusty from the damaged seal? Was there any scoring of the caliper?
Remove the pads from the caliper and try levering the piston back into the caliper. Does it move? If not disconnect the brake pipe from the caliper and then try and lever the piston back. Does it move?
This will determine if the fault is with the caliper or the brake line. If the piston doesn't move with the brake line attached but does with the line removed then you could be looking at an apportioning valve fault somewhere in the brake line between that caliper and the master cylinder. Locate this and replace it, then rebleed the system and test.
If the piston doesn't move at all with the line connected or not then you will need to strip the caliper down and reinspect. It may need replacing.
I assume that it is not the handbrake that is sticking on that wheel. Check this first as it will be the least amount of work.
Please let me know how you get on, if you have any additional questions then please reply.
Many thanks, Steve
hi there, brake locked up and had to bring to mechanic- caliper knackered so i never got to try your answers-thanks anyhow