By using fancy digital optic equipment, we found a small oil fountain from the connection between oil sump and bed plate in the area close to the oil pump.
But how difficult can that be? Just remove the oil sump and correct the error! Now this operation wasn't as simple as one could imagen, since the oil sump is part of the rear face of block, which means that the transmission had to be removed. And the propeller shaft, but first of all the transmission tunnel had to be taken out...etc. etc.
Ragnar, Anders and the precious one-zillion-bolt-screws Volvo 960 oil sump.
Here's the oil sump. But what was really the problem?
This was the problem. Around the hole to the left, there should be an o-ring (assembled in the bedplate). And there was none. Who was to blame? Who assembled the engine? Never mind....it's ok now. I've heard that it's only human to make errors.