+1 Sticky pistons you can sometimes free them up by removing the pads and the caliper but leave the hose attached. Then remove the boots and find a piece of wood about 1/2'' thick or thicker you need to just expose the dirty part of the piston. Using one of those cheap "G" clamps made out of flat bar clamp the wood over one piston to stop it coming out. Then carefully apply a bit of pressure to the brake lever to move the remaining piston out but be careful not to pop it out all the way. If you pop the piston right out you are in trouble and might have to replace the seals, so be extremely careful. Clean the exposed part of the piston with brake cleaner and possibly an old scouring pad that is not very abrasive. Once clean push the piston back in and repeat on the other side, keep on eye on the fluid level as you may need to remove some of the fluid. Holding the clean piston in with the block of wood and the clamp do the other side once both sides are done replace the boots and after pushing in both pistons replace the caliper and pads. With the caliper on but with the dust cover removed pump the brakes and observe the movement of the pads they should now be equal. While you are doing this you might as well change the fluid if it needs to be done.
Regards Martin.
