I think its my oil sending unit on my 89 300CE, but want to make sure before changing it.

When first start the car, it would take about 3-5 seconds before it get to 3 bar. During driving it would stays at 3 bar, but when I come to a stop, it still at 3 bar. Should it drop from 1-2 bar at a lower rpm and resume to 3 bar at a higer rpm? Am I on the right track or its something else that went wrong. Thanks.