Boost Leak at Brake Booster
 

Tracking down some boost leaks on my car (90 model). I found that I'm getting pressure leaking between the master cylinder and the booster. Based on my research, the NA booster is internally sealed and there is no gasket required between the master and the booster, so I don't think it's from that junction.

The 3 things I'm considering:
- Put a check valve in the hose to the brake booster. If the brakes worked fine before and my only concern is a boost leak, wouldn't the check valve stop most of the pressure going to the booster in the 1st place?
- Install a used brake booster. I already got one from ebay, but I don't have a way to bench test it to know I'm not just going to have the same problem again.
- Delete the booster. I don't hate the feeling of driving the car with the brake booster disconnected, as I've done some lately.

Has anyone faced a similar problem? Or are they any recommendations how to proceed? From what I can tell I have a totally stock braking system right now.

There is already a check valve in the brake booster line. So it could be that it failed.

Is it in the hose itself? Because if so mine is either failed or missing. I can suck/blow freely through the hose/pipe/hose that runs from the intake manifold to the booster

Edit- I did research on it. It's meant to be in the hose that runs between the vacuum pipe and the booster. Previous owner had used an auto parts store hose, so no check valve for me. Got a new OEM hose ordered.

You don't need a new hose.
There are 3/8" or 10mm check valves available for a couple of bucks.
Just cut the hose and add it in there with proper clamps.