Replacement Power Brake Booster Source for '68 Dart ??

Hey FABO,

Help Please!

Well it seems the inevitable has occurred: The mechanic is convinced the Brake Booster is dead! So where do I go to get a factory correct booster to replace my dead one? I saw a comment on FABO about a shop in California that does rebuilds on them and sent an email but haven't heard back (Covid...Christmas..Closed??). I guess I'd like to order one ASAP then send mine off to be rebuilt so I have a backup available down the road. Can anyone point me to a supplier of a unit which will actually have the correct bolt holes etc??

Background: Brakes blead up to hard pedal but when you start the car on the hoist and put it in gear then apply the brakes they won't stop the rear wheels from turning? There's an audible hiss from the booster when brakes are applied (I think there's an idle drop too, but no tach so Ill have to hook a digital tach up and test it myself?) Mechanics have tried 3 ways to Sunday to test booster and are sure it's compromised.

So where in Western Canada do I get a booster that will bolt in and work?

Thanks in advance.

1968 Dart Convertible, front discs rear drums, NOS distribution valve, Flintstone brakes.