69 weird brakes

Get a Mityvac and see if the booster holds a vacuum.

If it doesn't, take it apart and inspect the two rubber diaphragms.

If it's a correct '69 booster, you can unbolt the clamp and open it up.

I'm sure you can get a replacement diaphragm if you have a torn one.

I installed a charcoal filter in the vacuum line from the intake to the booster to prevent gas fumes from deteriorating the rubber diaphragms.

Dorman part number 80195.