I think the oil pressure gauge on my old 85' 380SE flickered a little at idle and that car had a low reading at idle. It had almost 300K, so I guess the engine was worn out. Fuel gauge on that car was steady as could be.

My old 84' 190D had perfectly working gauges. They were steady as a rock. Oil pressure was excellent, but it only had 152K- which is low for a diesel.

My current 88' 300SEL has a very steady oil gauge and has so much better pressure than my worn out 380SE (with much less 154K miles) had (its around 1.8 bar @ fully warmed idle vs .3 on my old 380SE), but my fuel gauge is crazy. It runs out of gas before it gets to "R", and even after 150 miles of driving after I have filled it up, it will still go all the way up to "1/1". Its very erratic.