mine 155 has got the same problem last week , in fact the oil pressure when warm dropped til 1bar.
I've bought a new oil pressure sender already , quiet expensive by the way 57€ , hasn't changed it yet .
I know it's although not easy to reach the thing , it ought to be a very easy task.
The thing that worries me is the following , if the old sender gots knacked when unscrewing , (the old one is fermly fixed ) the part that stays in the engine (very thin nut) can't be released anymore.
Anyway I change the thing tomorrow , hope it works out fine , like yours DG.