Gradual Oil Pressure Loss!!!

[HotCrew]

My friend has a 1983 Porsche 944 N/A.
He was driving and his oil light came on. While driving he gradually lost oil pressure. He knows there is a slight oil leak that drips oil on the drive. The car started to run funny. Added oil in case it was low but that didnt do anything. Oil pressure is high or normal after starting but loses it as he drives. Also right before the problem started he took it to a shop to have the oil changed but they didnt have a filter for it so he got it back without the oil change.
I havent looked at the car yet but how should we go about solving the problem? I am going to go get a shop manual for it. Can anyone send us in a direction? Thanks.

[HotCrew]

So i guess no one has any ideas other than what i have mentioned?

[Cbass]

If the engine was losing oil pressure due to a leak, it would need to spray volumes of oil out of the engine somewhere before you would see an appreciable pressure drop.

I would suspect the oil pump, although I am at a loss as to why the pressure would drop gradually as the engine warms up. I would recommend pulling off the engine oil pan, and visually inspecting the oil pump. If the oil pump is clogged, or has somehow come loose, this could explain the problem.

Good luck.

[HotCrew]

I figured it had something to do with the oil pump...when we figure it out i will post back.

[HotCrew]

So far we took a look and the dipstick is cover all the way with oil does that mean anything? I know we dont have too much oil in it. Could that be a blockage somewhere?

[83-944]

That's too weird. The dipstick would punch any plug back through. Excessive blow by might cause the oil to come up the dipstick tube but that's only if the engine were running. Please, keep us all posted.