oil pump relief valve query

[jp928]

Bought a 96 NA 8 in 2014, and shortly after lost oil pressure. Pulled the sump, found the pressure relief vave stuck open. Managed to get the piston out, clean up some markings on it, back together, OK since, except oil pressure is poor (real gauge) - never see more than 32psi when hot through.
So, now building a replacement engine from an ebay cheapy, doing whatever is needed. Its a 94 block, which is good, as it has oil feed source for the turbo. On pulling the oil pump (B6s8 casting) and pressure relief valve, gets curious. The piston is 25mm long, where a spare I bought for the other engine is only 18mm long. Also the long piston is marked in a pattern - vertical scratches from the top down the sides ~10-12mm apart, then betwwen those 2 marks a set of scratches start in a semi circle, go 5-8mm downwards. When I mount the piston on a tool so I can move it up and down in the bore, the scratches correspond to the sides and lower edge of the hole for bleeding off pressure. Looks to me like the piston oscillates abput 3mm as its bleeding off pressure. With the rotors removed, the bleed hole looks to have sharp edges, consistent with the scratches.

Any noticed this before, had bad experiences with the relief valve etc ?

Planning on fitting a BP4W pump anyway.

Thanks
jp

[jp928]

Back again.
See attached pics of long relief plunger showing scratches. Mate with skinny finger was able to get into the relief area, and could feel rough edges on the hole that is opened by the relief plunger opening.
The short plunger is a new genuine item, 18mm long vs 25 for the old one. Note also that it has a slot cast in the top, which I suspect will allow a small amount of oil to get to the sides, but not actually bypass any pressure. The old long plunger has a plain flat top.
Any thoughts ?

jp 92 NA6, 96 NA8 turbo