It felt like loss of power assist, but when I would pull the check valve off the boost cylinder, it would swoosh, like it had good vacuum 'stored' Twasn't until today that I realized when I switched the valve cover sides, to get the oil fill out in the open, I don't have anything plugging the PCV on the drivers side... Carb vac. line goes in the pass. side, and 1/2 vacuum leak on the other side ... That's another place to look for leaks if anyone was making a list.