My mixing elbow coroded and cracked to the point that it was leaking exhaust. I ended up fabricating something out of pipe fittings that seems to work OK. I would imagine you can buy a replacement elbow though somewhere. Using pipe fittings isn't perfect - for one thing I could not get the correct fittings to match the exhaust hose so I ended up wrapping the one fitting with fiberglass tape to make up the size difference so the hose would seal around it properly.
