BP - it's a safety valve - it only operates when oil at acertain pressure dislodges the ball from its seat. The spring that holds the ball in place can be tensioned by screwing the adjuster in and out - in (clockwise) to increase the tension and "jam" the ball harder against its seat.
If it is a Westach guage, the output voltage from the transducer of 0.5V should give 0 psi. And 4.5v gives full scale deflection.
So by disconnecting the transducer from the electrical plug and putting 0.5v to the output the needle should lift off the stop and read 0psi. Up the voltahge to 4.5 and the needle should read fsd.
You'll now know if your guage functions.You can test the transducer in a similar way with amultimeter and an airline.
Don't ask how I know this!!
Allegedly oil cavitation on bearing shells leaves strange witness marks on the bearing face - a bit like corrugations.