I would try Locktite 510 flange sealant I have used it several times for jobs such as this, it stays soft until under pressure, if you have a big gap then I think you should try and shim it first.
The housing needs looking at carefully...mine had ended up as an elliptical quartic plane curve in cross section...it was never going to be possible to get anything to sit square and central in it :grimacing:
