Master cylinder replacment?

[M.L.S.C.]

Ah, okay then - for some reason I thought you pulled the hose off the valve and plugged the hose, while you actually pulled the valve off the booster and capped the valve - at that point I'd agree with you that the low-vacuum problem is booster related, and go ahead and replace the booster.

[AK94]

So how important is it that the booster be replaced right NOW? Can it wait a while? Can this part really FAIL? Or would it just slowly go out?
I would think that it is not a huge safty issue because I would think it would slowly go out. But I have been wrong before.

[M.L.S.C.]

Dunno man, I'd hate to tell ya you can keep using it and next week it fails on you and you slam into the back of a semi or something. I can tell you that much - stopping without it will be a very interesting moment - I once broke the check-valve of my old truck while trying to remove it to check for vacuum leaks, so I had to drive home stopping on manual, not fun at all, especially considering it was a halfton with stock brakes but rolling on 35s. Tis you call really, but if anything at least find a big open parking lot and pull the valve off the booster and practice some stops, so you know what to expect should it fail on you while you drive.

[AK94]

Well, thanks a lot for all the help. I guess that I will just replace the booster as soon as possable. Any tips on that job?
I'll let you know how it goes and what the result is.

[M.L.S.C.]

Tis a pretty straight-forward job, getting the booster rod off the pedal may need some persuasion, but it'll come off eventually.