is there any way to test the brake booster?
 

i'm in the process of working on my 93 fd. trying to get the engine bay nice and clean and looking great while the engine is out. for awhile i've noticed a rusty spot on my brake booster and the other nite while working on the car i removed the brake booster and noticed more rust toward the bottom of the unit. i bought the car as a project and have never been able to test the brakes so i'm not sure if they work fine or not. i know the brake fluid reservoir was very low on fluid. i'm wondering if there's a way to test the brake booster before i begin reassembling it.
yesterday i took off the reservoir, mc, and associated brackets and sandblasted everything so i can repaint them. i've started painting the parts but, now i'm wondering if maybe the brake booster if failing or bad. i'm just wondering if i can test the brake booster some how before i finish painting and reassembling everything.
anyone have any ideas? when i took off the brake booster i pulled the master cylinder and noticed the O ring on the end of it. should that be replaced when reassembling?

Generally speaking...you'll want to put a vacuum source on to it to make sure it doesn't leak.

its pretty simple, put a vacuum on it, and it should hold it.

so do i need to reassemble everything and put some fluid in the res then do this?

nope....not if all you are testing is the booster mechanism.

The booster is a completely separate mechanism from the brake master cylinder, of course. The master cylinder is a whole 'nother animal, and much more complex. And yes, it is a good idea to replace ANY 'O' ring/seal when