Volvo: Volvo S70 GLT, volvo mechanics, metal sludge

Question
I have read most of the low/no oil pressure questions and noticed one from Joanne (8/29/2007) that sounded similar.  My oil pressure light started coming when starting and stayed on for a couple of minutes.  A few days later it start to flicker while traveling on a trip.  It then eventually stayed on.  I stopped and checked the oil level...okay.  I drove it after conversing with mechanics on the phone and believing it was the sensor.  After 300 miles the car was running good but the low oil pressure light was on all the time.  I took it to a mechanic and he measured the oil pressure with a gauge, it was 0 psi!.  He check the gauge and sensor, both were good.  He took the pan down, oil was clean no metal, sludge or anything abnormal (I changed the oil regularly...172,000 miles) and had every Volvo service recommended. He talked to Volvo mechanics, bought the o-ring kit and changed all the o-ring's and seals, including the pick-up tube, oil cooler tubes, etc..  Now I have 5-6 psi oil pressure.  Took it apart again. Pulled the oil pump..looks good.  Changed all the seals again...no change, 5-6 psi and oil pressure light still on.  You can see oil splashing on the cam when the filler cap is removed.  They used the special sealant on the oil pan and had it chemically cleaned before resealing.  They wrote mechanics on-line and talked to 2 Volvo mechanics.  He is an experienced mechanic who has a friend who is a volvo mechanic.  They talked on the phone and when through each seal/o-ring to make sure he didn't miss one.  I now have the car back after 4 weeks.  There is no change.  The deviation from normal maintenance was the last 2 oil changes were not by Volvo including this one and I do not believe they used a Volvo oil filter. It appears I'm getting oil flow, but no pressure.  You would of thought this engine would have failed by now.  Any ideas at all on what to do next?

Answer
Mike,
With the mileage and the work already done I would consider a rebuilt or used engine. By now I would say there has to be a certain amount of wear beyond the norm. There is a bulletin about a leaking oil pump but nothing about low oil pressure. Your only other choice is to go over the work already done and inspect those seals and o'rings.