Year and mileage. Did you register the 1 bar at cold startup or after you drove it around for awhile. Looking at the cluster, I think it is the R129 90-95 sl. If so, it would be equiped with the M119 Motor. I have had two oil pressure problems with my 99 s420 and the dealer replaced oil pump and oil sending unit. If this is the problem then it shouldnt cost more than $700 to fix. If you got 1 bar on a cold startup then something is very wrong. How did the needle move, did it quickly pin to 3 or slowly?