Had to fettle the back brake on my kinesis last night, one piston was a bit sluggish. Extending the piston and a wipe/lube with mineral oil sorted it out. A bit late now but I found a rather good howto with pics. It's for Hope brakes but should be useful for other brakes too, most calipers are similar design nowadays I think.
Those pics show you just how bloody huge those M6s are, proper DH stoppers. Gonna have to do some more tinkering soon, got some old brake hoses that need changing but hope have changed the hose sizing 6mm->5mm i think, £20 for the new connectors! Per brake! Ouch.