I decided to check the vacuum pump again before replacing the booster, and now I think it may be a problem with the pump. The first time I checked the pump it pulled a steady 22 In Hg, but this time the needle on the gauge was bouncing around violently around 5-10 In Hg. I pulled the pump and the diaphragm looked OK, but wondering if it could be a bad check valve? This pump has the internal check valves. Does anyone know if I could replace the internal check valves with external check valves, or where I could get replacement internal checks?