Originally Posted by christuna

Since you mention in your first post that it all started when you did all the work at once (master+booster) and from reading what you diagnosed (good vacuum at the end of the pipe and o-ring at master cylinder) AND you tried 2 boosters then the only thing that I can think of is air in the hydraulic system.

I could be that the no shutoff you're experiencing is caused by a leak in the shutoff system that gets worse when the booster is hooked up.

did you use the foot method? gravity? a power bleeder?

did you bleed the master cylinder before installing it?