Recently completely rebuilt 55 Merc 292.  Engine has approx 300 miles and I noticed oil underneath rear main area and dripping out of crank breather tube after driving.  Installed a cheap oil gauge that reads 0-to-80psi and engine reads 60 at idle and about 78 at rev-up.  (probably max for gauge, pressure may be higher).  Should I change oil pump?  If I make the change how will I know the replacement won't be the same?  Oil pump new and installed by machine shop during rebuild.

Thanks, any help appreciated.

Gary