[bobcowan]

As said above, there are two common places for leaks.

Remove the o-ring, and lightly sand the gasket surface. Place some fine sandpaper on a piece of glass, because is usually the flattest thing in any house. Look at the gasket surface for high and low spots.

The screw in nipple for the bypass hose is also a common spot. 6 years ago I put mine together using JB Weld and pliers. Still going strong, no leaks.

I don't use a gasket or o-ring. Just a little bit of silicone sealant.