I just had my '82 240 diesel wagon aligned after getting it running again. It had been sitting for almost three years. The car runs great now but has an odd steering problem. When I let go of the steering wheel the car will drift rather sharply to the left. The mechanic assures me that the alignment is correct and the tires aren't showing any unusual wear after 500 miles. He told me that the rack is overboosted to the left because the proportional valve in the rack needs adjustment. He's a very good volvo mechanic but even he has no knowledge how to make this adjustment.

Does anybody know how this is done or should I start looking for a replacement rack?