Hi Jim
Over the years there have been numerous threads talking about the brake assist or Booster. So start with a search on the word "booster" that it will give you some pictures of what the unit looks like. Which I think will help narrow down your efforts to get your brakes working.
Here is a good thread to start with as it has pictures of the booster.
http://www.mapleleafup.net/forums/sh...ter#post220149
From experience can tell you that just because the brake system doesn't leak dose not mean the brakes will work. You need to confirm that each wheel cylinder is actually moving both brake shoes. I learned the hard way when I first got my HUP many moons ago. Topped up the brakes it felt like I had brakes but when I stomped on the brakes the HUP turned violently right.
Cheers Phil