You are looking for a minimum of 12.5 psi at 750 RPM and a maximum of 67.7psi at 4,000 rpm. The only way you are going to really know if it is right is to have someone check the pressure. To do this you need to unscrew the oil pressure sending unit and screw in a pressure guage and check it. I guess another option would be to buy a new sending unit and screw it in and see if the light goes out or not, the odds of a brand new sender being bad are pretty slim. The reality is that you probably need to have all of the O rings in the oil delivery system replaced. All of the white engines do it to some degree, some are worse than others. Do you have any "ticky ticky" noises coming form the motor? I had an S-80 in the other day that purred like a kitten (125,000 miles) but it was flashing the no oil pressure message. I took the oil pan off and sure enough it had spit one of the O rings on one of the pipes right out. So the pump was sucking up the oil, stuffing it through the filter and on the way out of the filter it was puking all of the oil back into the pan instead of pushing it throughout the motor. Real typical stuff, see it all the time. In a Volvo shop it should run in the area of 3-4 hours labor and about 50.00-75.00 in parts.