Power brake booster

I'm fairly sure the booster in my Impala is toast, it's 40 years old. When I stop and idle in traffic it hisses, sometimes the hiss would stop if I pushed down harder. The car is running terrible lately and my friend seems to think it's a vacuum leak from the booster contributing to this. I have to plug the hose and see if it changes anything.

At the same time, my master cylinder is going. It droops a little every few seconds when you're putting your foot on the brake with any form of consistency...this was happening for a while but only got bad in the past few weeks. It's also original. The brake warning light even comes on, but if I pump the brakes and push down hard on the pedal, the light resets itself. There is no real external leakage, but I'm almost wondering if any fluid is getting sucked into my booster and then into the engine.

I already got a new Wagner M/C (the damn thing turned out to be a Chinese part, wtf..) and I'd like to replace the booster at the same time. I have heard bad things about getting parts store reman boosters, and there is a guy names Steve Gregori out in CA who seems to be the go-to guy for brake booster rebuilds, like 155 bucks for a full resto. http://www.brakeboosters.com/index.htm
There is also another guy: http://www.boosterdeweyexchange.com/ My original booster is one of those "Delco Moraine" stamped units so no matter what I would be keeping the old one just in case.

I'm worried about taking this out myself though, because I sure as shyte do not have a place to be bleeding brakes and such, the M/C ain't gonna be done by me. But, I am wondering if I can just unbolt my M/C with the lines still attached from the booster, move it forward gently, and get the old one out so I can send it to be restored then put it back in the car, I dunno. Has anyone ever had to replace their booster? What did you wind up doing?

I don't know if it helps but, I recently did a brake booster on a F150 and I was able to leave the M/C still on the lines and just did the booster. I guess it will depend on the amount of room you have.

Power booster can come out with out having to disconnect the lines from master cylinder. only a rod hangs out the back of the m/c. The booster should be held on by 4 bolts. I did one in the 80 caprice I had. They all work the same. If you dint have any external leaks you may be leaking into the booster, And you might also just have a blown seal inside the m/c. Did you check the wheel cylinders? I assume you have 4 drums ( at the least 2) if it's leaking out of one of them it may just be leakin into the drum and while driving drying out. Are you actually losing fluid from the reservoir? To check the booster for a fail, turn the car on and pump the brakes like crazy, turn off the car and go under the hood and pop the plastic plug from the booster (don't just undo the hose) if it pops with a POP like it was under pressure then it's still good. check the hose and the seal for damage, dry rot.

Good to know-

My car is front disc (I think they started doing that with the very late 60s models or 1970 maybe).

The M/C looks a little damp right around where it bolts onto the booster. I haven't noticed anything running down the insides of the tires and whatnot, this car had a blown rear brake line when I bought it and then it happened again about a year later on the other line (neither were very rusty oddly enough, just one spot) so I've had my fair share of looking for that issue. I've never had the drums off though, in fact they have never been removed from the car, the rear drums still have those little keepers on the lugs that held the drums on during assembly!

I did check the reservoir a few times, the rear brake res. is about 1/4" below the level of the top of the m/c body, hasn't really gone down. When the brake pedal droops, I can quickly pump it and it will be hard again for like 5-10 seconds then it starts to droop a little again...if I leave the car in neutral so I don't have to push down as hard on the brakes to keep the car stopped, sometimes it won't even droop at all.

I think I will price a booster from Napa or something...if the price is high enough compared to that guy who rebuilds them, I may just go the route of shipping it out to be rebuilt. It looks like crap as it is right now anyway...lol. I'd like to have the car fixed as quick as possible though too so I can drive it and concentrate on what I'm going to do about putting a functional radio in there...

https://napaonline.com/Catalog/CatalogItemDetail.aspx?A=NBB5481115_0136006655&An=599001+101974+50012+2012032

Doesn't seem like a bad price. I wonder if it's the same price going to the store and buying it...I think the NAPA ones are reboxed "Cardone" boosters, which sell for like 15 bucks less on RockAuto.com, but then you gotta add shipping and the warranty through Napa might be easier to deal with since they have a brick and mortar store location you can just walk into...I know if I sent out my original, it would be a few weeks downtime and at least 50 bucks more...