Oil Change Causes Oil Pressure Problems?

[ezrider]

I am the original owner of a 1991 350 SDL with 159K miles on it now. I had my oil changed recently at my local MB dealer as I have done many times in the past. The engine has no history of oil pressure, or any other significant problems.

When I picked up the car after the oil change I noticed the oil pressure gauge twitching a little bit at idle, I have never noticed this before. Yesterday after 350 miles the pressure dropped to near zero at idle and "2+" on the gauge at 2300 RPM and above. It was always pegged at "3" at anything much more than idle in the past. I believe the gauge because I can hear some lifter noise at idle that has never been there before.

Today I had a ex-MB mechanic, now independent, evaluate the problem. He found the "O" rings on the oil filter stem rock hard and said they should be changed with each filter change. He changed the "O" rings but we did not get an improvement. He says the oil pump could have failed due to starvation caused by the old "O" rings. He said my hard "O" rings could be the root of my problem. He confirmed that my oil pressure is a problem and is hoping a new oil pump will solve it, but that it could be worse.

He also suggested that I talk to the MB dealer that should have changed the "O" rings and didn't.

Has anyone here experienced oil pressure failure due to these "O" rings?

I would appreciate any advice on how I should approach the dealer.

Thank you.