All moving parts are in great shape and slide easily. Caliper piston won't fully retract. The vacuum pump test sounds promising for checking the hoses. Do I connect to the bleed valve to extend the piston, then remove the hose and apply vacuum to the end of the hose? I would think that if upon removing the hose, the piston would still resist moving would be an indication that the hose was bad. If on the other hand the piston moved freely, that would indicate that the problem was further upstream than that hose. I've been reading the workshop manual and found that the master cylinder could be a suspect. I'll probably start by changing the hoses first anyway. Does anyone think that the abs control unit could be the problem?