I am now in the derek uk camp.

I rebuilt my B20E about 8 years ago. At the time, I inspected the pump and checked the end float on the gears (not easy to do) which is the primary spec for the pump. I also installed the IPD reenforcing ring and high pressure spring. Fast forward to last summer when everything was fine, then it wasn't. About 10 minutes into a fine evening drive the warning light flashed on my oil pressure gauge indicating low oil pressure when idling at a stop sign. Revved the engine and oil pressure recovered; but, it reoccurred at the next stop and at every stop on the way home. The next day I did a cranking oil pressure test to check my electronic gauge and got no material oil pressure at all so the pump or something related to the pump was dead.

I removed the existing pump from the engine and inspected it . The end float on the gears was at its upper limit; but everything else appeared normal (the oil pipe seals were all in place and in good condition) . There might have been something in the check valve holding it open and allowing oil to internally recirculate at low pressure causing the sudden loss of pressure. However, when I removed the spring and checked the ball it appeared to be seating correctly and passed a pressure test. I ended up replacing the pump with a new Melling cast iron pump that I got from Rock Auto (lower cost than the Volvo pumps which are made from aluminum). Put everything back together and everything was fine so the problem definitely was pump related.

The only thing I noted on the pump was scuffing on the end plate. That might have been caused by the IPD reenforcing ring which was a very tight fit and may have pushed the drive gear down slightly. I ditched the reenforcing ring when I installed the Melling pump. If you are thinking about re using the pump, make very sure that your end float measures out on the tight side. My experience suggests that if the float is approaching the upper limit you are going to have problems.

Final note, on my 140 I did not have to remove the engine to replace the pump. I built a fixture out of 2x4s ( a copy of the special Volvo tool described in the service manual) to raise the front of the engine a couple of inches which is all that is required to allow pan removal. I expect the same process would work on the other vintage Volvos as long as there is room available at the back of the head to allow the engine to be pivoted up on the transmission mount.