Never been real happy with the rear brakes on the XR400. Seems to lock-up and stop okay on the dirt, but not much stopping power on the road (I put this down to the Knobbys).
Anyway, thought I would do the piston and seals and discovered some slight scoring in the piston sleeve. Piston and seals seemed okay - any views about whether the scoring is likely to be impacting the brake function and is it bad enough to replace? Sorry the pics aren't real clear, but the scoring can be seen and felt. Cheers.