Vauum leak? Brake booster and shut-off

[danderso]

Hello everyone!

it's been years since I've posted on a forum; used to post up a lot in the Volkswagen forums few years back!

I have a 81' 300TD Turbo, after doing a valve adjustment I noticed that the car was shifting a little lower in the rev range. After doing some research I decided to adjust the bowden cable, now it runs like a champ!

On my test drive, I stopped on a hill and went again. At which point I pressed the brake pedal, and it was rock solid, like the brake booster was no longer functioning. SO I brought it back, and went to shut it off, and it kept running! These two things point me towards a nasty vacuum leak.

I checked over all the obvious vacuum lines, and they appeared in place. So I started the car, and it the brakes were fine, and it shut off reliably for about 15 miles or so, then it decided to repeat the symptoms.

Where should I start looking?