FWIW & IMHO:
Just my own opinion here and no flaming intended, but I would not change over to vacuum on a pristine low mileage car and with only 31K miles, I ASSume that the car should be very pristine.
I would definitely find out what is causing it, though. I don't think that driving it only once a week is the primary cause, as sometimes I don't drive mine for a period of a couple of weeks, and occasionally more, and I have only lost one powermaster, and that was on a '87 Trubo Buick with about 90K-95K miles on it. Over a period of close to 10 years, and 5 '86-'87 Turbo Buicks, (1 '86 & 4' 87's), it has been my personal experience that you will lose about 2 powermaster brake accumulators to every 1 powermaster unit. Somebody at kirban Performance Products wrote that it is paramount to keep the fliuid clean, and to change it quite frequently. I don't remember what he said that the recommended change interval was, but it seemed very frequent to me. Are you checking the fuses when you lose the brakes, and what went out on the other powermaster units would be helpful in chasing down the reason. Look for a leak somewhere if the motors keek burning out. I would never replace a powermaster with a vacuum set up on a low mileage car like that. Ever considered Autozone & some of the other places that sell re-manufactured/rebuilt/re-furbished units that are guaranteed for life. I do not like to put rebuilt stuff on my cars but I would sterongly consider it in your case. Also, keep in mind that GM Parts Direct sells a unit for about $ $ 585, but doesn't say if it is a new or a re-manufactured unit. It was brought to light by "Turbofis638" in a response to another thread that it might be a unit built by either Raybestos or Bendix, and not by AC-Delco, and that would explain the almost half price compared to the dealers. Do as search under "Wells" and find "Turbofisn38" response to "GM Powermaster part no." and another search for "How long did your Powermaster last?", both on this board.
Sorry for t4he long post.
