96 (n-reg) rover 400?

rear brake is working fine but somehow the handbrake is not working on one side, the spring itself is ok and can see movement on the outside of the caliper??? after a very close inspection i believe that the spring must move something inside to push the pistons on to the disk, could i be correct that either something has snaped inside or could it just be the seals that have gone??? never worked on a hydraulic handbreak before, thanks in advance!!!