Thanks all for your input.
First to clarify, it is the pressure relief valve positioned to the front/right of the engine. When tapping out the valve I put the aluminium tube in the hole where the oil pressure sending unit goes so all that shrapnel was pressed down towards the valve.
I don't have the bearings at home, so no images of them, but I can assure if they've lost big chunks of material we would have noticed
Another clue to this mystery is that I took one of the small flakes and held it to an open flame of a candle, just to see if it was magnesium that I know would burn. Instead it melted instantly. So I would guess lead or tin...
Where could some soldering come from? The oil cooler? It looks great and have no signs of leakage but with this info I will take it to someone to test for flow.
Also, I have removed the oil pump, taken it apart and cleaned all parts before reassembly, no problems there. Not a sign of shrapnel there or anywhere else in the engine.
Could it have been a oil sending unit of a questionable brand. Or some PO-hack job on that end?
Appreciate your input as always!
//Jörgen