Common issue
The Brake Booster seems to be a common issue that will fail after some years of use.
I just had my power booster rebuilt along with the master cylinder (but my MC was too gone to be rebuilt, so I had to replace it with a new one).
Here is a little advice from my experience...
Be sure to take the breather check valve off the booster before sending it in (keep it with you!). I did not and they sent it back with a different single output port instead of the dual port valve I needed. (one line to the manifold, the other to the transmission). This created unnecessary troubleshooting and wasted time trying to resolve getting the correct dual port breather check valve again (and please note that no local chain parts stores carry it, so you have to special order one...!).
I recommend stripping most parts off anything you send in to be rebuilt. If they don't ask for it specifically... keep it in your shop.
