My 1995 E320 wagon has shown no oil pressure for two years. The gauge reads normally when cold, but 5-10 minutes later, I get zero at idle, and 2.5 to 3 above 1500 prm.
If you let it sit and idle for 5 minutes you would expect a lot of niose, at least lifter noise. not the case.
Most likely it is the sender unit. The shop told me the sender is a ***** to get at, so I decided to foregt about it. Two years later, with 191k on this car, it runs great. I suppose this will be an issue when I sell the car.
Until then, Don't Worry; Be Happy.