The piston closest to the hose is fine, the other one sticks. If I hold down the good piston and pump the lever then the stuck one moves but otherwise it won’t budge! Stripped the caliper and cleaned it and the piston with IPA then lubricated the seal with silicon lube. Reassembled and bled but problem persists. What now? New piston & seal (they didn’t seem damaged though)? Or try again but lubricate the seal with “red rubber grease” (saw this in another thread. Didn’t have any to hand though)?

bump for the morning crowd

Grease would be the obvious choice. The piston kits are about £10 from uk bike store so it’s worth a shot. I know when mine were knackered after Kielder 100 it was simple job and made the world of difference. After the service they perform like new again.