I'd recommend to buy a pair of used brake calipers from the Yamaha XJ650. Repair kits can be ordered at kedo.de, the one for the SR500 fits. They have also the pistons, but i think a used pair of calipers is cheaper than 2 pistons. Article number 40161 and 27834

Bye,
Georg

Hi everyone
I have found a piston and seal kit at www.bitzforbikes.co.uk at 30 euros for each kit which is piston and seals, the kit is tourmax 283841 (cpk-109), I have recieved these and they apear to be a direct replacement.
Regards
Tony