How do I troubleshoot my brake booster?

I would buy new/ rebuilt IF you can get a decent one and "look alike." The reason is warranty. Master kits have always been somewhat expensive, and if you buy a kit and find out it won't fix it, you have dumped a fair amount of money that a complete master costs

Be sure to follow destructions re: "pre" bleeding or "bench" bleeding the master. They have to be sort of "primed" to get air out of the piston area.