Although I usually put Chevron Delo-400 15W-40 in my '85 300D (W123, OM617), I have used Mobil-1 5W-40 and I don't recall any significant difference in oil pressure at hot idle. The factory says anything over 0.5 bar is OK at idle but the pressure must climb to 3 bar at engine speeds above 1300 RPM--as was said in an earlier post.

Definitely change those little o-rings and make sure the inside of the pipe isn't clogged. You can also squirt Brakleen or whatever cleaning solvent you use into the pipe. Because the exit hole is so tiny, you have to give it time. I rigged up an adapter for my air compressor that allows me to attach a piece of heavy plastic tubing to the end of the pipe. With the air pressure set to about 5 psi I can go away and let the old oil and crud gradually ooze out of the little hole until nothing comes through but air.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970