I seem to have a similar problem.. Is this the same on a CB750 K2 ?
My pistons aren't retracting. I removed the passive side and the brakepads and when I moved the lever the piston moved out as it should. But when I removed it It's impossible to push the piston back in, this is the same for both calipers (dual discs) and they where cleaned and new seals this winter. Ill try to aply a pressure then loosen the banjobolt and se if it retracts, by what I have read, that would indicate that the MC needs a overlook hence not releasing the preassure.
but where the f*ck are these small holes ? I look and look but can't find them anywhere. So if someone could provide a picture of the location of them that would be great.