It looks like the Sigmatek pump in my Comanche is finally dying for real. It was installed 5 years ago and we've been dealing with it reading low intermittently for the last 2 years by adjusting the regulator at annuals. In IMC this time it decided it wanted to put out 3.5" at 6kft and 23^2 which is way out of spec but its mostly OK on the ground. Oddly all of the instruments read well enough to continue the flight without being "nogyro" At 9k its down to 3" so clearly something is wrong. Now comes the education part, Aircrsftpruce has a variety of replacement pumps and it looks like there are 3 groups of dry pumps out there: *Rapco/Airpower which can be used as cores of one another and are really cheap *Tempest which doesn't deal in cores and nobody will accept as cores so I assume there's some internal difference. These aren't really cheap like the Rapco pumps but they are reasonable *Sigmatek which also doesn't deal in cores and nobody will take them as a core, these are double if not triple the cost of the prior 2 My questions are: 1) How do the 3 groups differ? 2) Is the Sigmatek worth it? Longer term how do you help a vac pump last, since this one died much quicker than the one in the Warrior I flew.