Id say 12psi was a little low.....15-20psi is preferable...mine runs at 20psi on SAE30 hot or cold....I did used to run on SAE20 but these hotter summers meant that it was running at 15psi on a river....so changed the grade.
My main concern would be if there is wear in the mains on the crankshaft as JP2's...especially marinised industrial units that dont have a forged crank...can break crankshafts due to movement.
One other possibility is that the oil pressure relief valve hasn't been set properly but be wary adjusting this as while you might get a higher pressure reading it wont solve the issue of worn bearings....
All this is of course dependent on the pressure gauge being correct....and depending on the scale of the gauge that might not be the case.