I've gone through 3 masters in 4 weeks. They're "Rebuilt" units from Murrays and the same thing happened with all of them. They work well for a couple days then one day, straight to the floor..(this last one started leaking from the back at the booster)
They're all for a 91 Caravan, 1" bore, correct prop valve, new brake parts front and rear, new fluid, new rubber brake lines and properly bled.
I'm going to go to Napa and see if I have any better luck.
Any tips? Should I go to a dealer?