380 SL Oil pressure gauge

I thought I would try for some advise on a problem that doesn't seem to affect the car's performance but is a aggrevation. I have a 1984 380 SL that when warmed up (about 30 minutes) has the oil pressure guage show 0 (Scale 0-3)when I have the car in drive and at a stop. If I place the car in 'park' the reading goes to about 1 1/2 (which is correct). When I accelerate, the reading goes to max (3) until I come to a stop and we start over again. The oil sender unit has been replaced twice (I thought the first replacement was bad also) with no luck. The car really functions fine with pressure etc. the first 30 minutes or so then crapple on the guage. Any suggests on this pesky annoyance?????

My 1985 500SEL oil gauge goes crazy at idle- vibrates like a tuning folk until I press on the gas, and then it goes to "3" and stays there until the next traffic light. I just keep checking my oil, and just ignore the bouncing red thing on my dash.

My 79 450SEL acts almost identical to yours, except that at a stop in drive it usually dips to around 13lbs not 0. Ive had it checked and pressure is always ok, so Ive lived with it.