Took my rears apart yesterday and found the boot on both left and right pistons had cracked, with the piston being tight on there. Managed to free them though and with plenty of cleaning the pistons came out ok. Some discolouring but no pitting that you could feel or see. Rebuilt them with new seals etc and they seem to be working like a charm
Also got front rebuild kits but ran out of time yesterday so will do that another time.