[DanEC]

Actually I shouldn't be so negative on trying a Mityvac. Most of the issues I've had with loose bleeder valves has been on replacement brake calipers which get rebuilt over and over again. I would guess not many slave cylinders are remanufactured from cores so no reason to think the bleeder screw threads should be worn out. If you have a Mityvac then it might work just fine. You could put a light dab of non-hardening thread sealer on the bleeder valve as a precaution.