I have just re-furbished my front calipers, then treated them to new disks, pads, brake pipes and flexi-hoses.
I put the caliper on the bench, removed the rings and dust shields then blocked off one opposing pair of pistons with a wood block and clamped the third piston (with wood and a clamp). I then blew out the fourth piston with an airline, protecting it with a rag.
I cleaned the piston and its cylinder and put the piston back, using red grease and some brake fluid.
Next I clamped off the cleaned one and released on of the others. Then I blew it out with the airline and cleaned it up.
I repeated this until all four had been done.
I then covered all four cleaned pistons plus the bleed nipple with masking tape, wire brushed the caliper and sprayed it with silver Hammerite.
When dry, the masking tape was removed, all pistons blown out a short way and re-cleaned and the cleaned-up rubber seals fitted.
You are right - fitting the rings is a PITA, but I managed it without super glue (took me a couple of hours though

). I resorted to pinning one end down with a small screwdriver, spreading the other end with snipe-nosed pliers, while keeping the loose coil pressed down with some spare fingers. I think they will heal soon
I made up new brake pipes using 90/10 cupro/nickle pipe and new pipe nuts. I replaced everything back to the brake pipe coil that allows for body lift/roll. I put Copperslip on the pipe under the pipe nut and wrapped the pipe nut thread with PTFE tape to stop it siezing.
This, together with new calipers, disks and so-on on the rear mean that the brakes are now good (and the handbrake will lock the rear wheels if I want it to

).
MOT on Tuesday, and as usual I'm feeling like an 'expectant father'
I have pictures if anyone is interested in the process.
Worth doing now, while the weather is relatively warm.
Bob.