I think your engine is fine as low as 0.3 or 0.5 bar at idle. It should peg at 3 above idle.

Part of the problem could be the oil. I don't think any -30 oil is approved for modern MB engines above 10C/50F. xxW-40 and xxW-50 only. Or maybe it's that cold where you are.

It could be a problem with the gauge. Have a shop temporarily hook up a mechanical oil pressure gauge.

Sixto
91 300SE
87 300SDL
83 300SD