If it comes down to having the booster rebuilt, I would highly recommend DS Parts Co. in Bluefield, VA.
dspartscompany.com They rebuilt the Midland Hydro-vac booster in my '61 5000 three years ago. It was an oddball booster that I couldn't find any parts for. They had them in stock and it was shipped back within a week 'n a half. Excellent service....
Not sure how that would work shipping from North of the boarder, but if it's justifiable...
Almost guarantee if you get that booster working you'll have good brakes. I've come up on red lights quick with my 5000 and if I stomp that pedal it'll bring me to a halt real fast!