Replacing Brake Booster?

[C15_Sierra]

After I got exhaust on my truck, I was finally able to diagnose why I wasn't feeling any power assist on my brakes. I have a pretty strong vacuum leak in the interior of the cab (sounds like the blower motor, but sucking) which the diagnosticians of the interwebs have told me is a bad diaphragm. Engine performance isn't affected, further leading to a diagnosis of a bad diaphragm

My truck had manual brakes and I bought a used booster and M/C to convert to power brakes. M/C was bad so I replaced it, now I'm guessing the booster is bad That right?

There is a boot that goes around the pedal rod going into the booster, and it sounds like it might not even be on tight. Can that be not seated right and cause issues, or is it definitely a bad diaphragm

Wish I could figure this out on my own (and earlier) but my boss sent me to NC for a few days on business on the day I got my exhaust fitted. So I didn't have much time to diagnose, and I want to get the right parts ordered before the weekend (not like it will help much)

I just want to drive my truck!