Since converting my 2 GN's to vacuum brakes, I've been through 4 brake boosters. I've put in a new check valve with each booster change. It's not really costing me anything, since I have returned one each time under warranty at Autozone. It's just a hassle to change and nerve racking when the failure occurs in traffic, like the booster on my 86 did today. Luckily I didn't hit anyone, but I did go through the light. Has anyone else had this many failures? It's almost enough to make me change back to the Powermaster setup.