Fitting a Mk4 Zorst.

Swaped zorsts round from my cabby to the XR3i cus the XR one was rotten to hell. Fitted it, and about three days later it starts blowing again.

So get under it, undo it, re tighten it, all is fine. then a few days later is it blowing again.

Now its just awful. Any guys got any tips to help stop it from blowing? Talking about the flange joint at the bottom of the downpipe.