Replace it...we are talking about the rear exhaust box aint we?..
I have had them repaired in the past..unsuccessfully..
You in the uk?
You could weld a slightly larger Ø piece of pipe on the box, 5cm / 2" is enough, make some saw cuts in it, insert the broken pipe and tight the bigger with a clamp. That should make it for a few months, even more …
BRs, Bernie
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Probably a bit overkill to get something to last a month. the standard pipe i believe is 52mm anyway.
If it's rotten then it's going to need replacing and exhausts are reasonably cheap and easy to replace at home.
BTW a fairly skilled welder would do that easily with a MIG.