[:'(] ouch hate it when that happens!

a common method for using JB WELD is as follows:
clean REALLY clean with solvent the edges of the break.

use some 1/16 scrap balsa and glue it with A LITTLE ca to the inside of the exaust port.

then apply some jb weld (only use the original not the "quick" stuff)

after about an hour it will be slighty firm, gently shape it to conform to the flat surface the muffler sits on using a small file. BE GENTLE then set it aside for a couple days to cure

then use your exacto knife to remove the small balsa DAM the key is to get the alum totally oil free

we did a club demo of motor repair with this method using a badly crashed LA 40. it had busted off lugs and a crack in the case full length of the lug and busted out screw holes. i would have canned it but we fixed it and so far it has run just fine.