I'm having trouble with the oil pressure light and buzzer coming on.
I'm wondering if the collected wisdom of the list might know if this is because of over-sensitive oil pressure senders?
Could it have anything to do with the type of oil filter being used? I remember debates about oil filters and pressure on vanagon engines. Does the wrong filter make pressure low or high? 
Any guidance would be appreciated. 

The background info -engine is a low mileage turbo diesel (140, 000 km) with new 20W50 oil and filter and a brand new pump. Rod and main bearings have been inspected by a couple of experienced mechanics. No apparent damage despite 3 episodes of the light coming on.
Light and buzzer comes on only when engine is hot (normal operating temperature) and after working fairly hard 3,500 -3,750RPM for five minutes or more. Then comes on when the RPM drops - coasting to a stop at an off-ramp. On another occasion came on when the rpm fell below 2,000 after cruing at 3,500 or more. Then when RPM went back above 2,000 it went out.
I've installed a Hastings electronic oil pressure gauge and it agrees quite closely with the mechanics gauge. 
I get 29psi at 2,000 rpm and it goe up from there.
Below 2,000 rpm it falls quite low 5psi at 1,000 rpm and even lower at idle 800rpm.
Pressure at cold is 75psi or more.
I don't think this should make any difference but this engine is out of a 93 Jetta turbo diesel and is now in a 93 passat turbo diesel.

Alan