I used some 2 part epoxy putty, you
kneed it till it's gray and press it in, I
have seen this as gas tank repair also.
I replaced a Radiator with a new, tho
crapily made Brazilian one, only about
$100, but the aluminum crimped part
started to come un crimped

So I
crimped it back and used the putty on it,
been holding for over a year now, but
get it clean before you start, also take
a little bit of the putty and rub it into the
spot to clean it and make it stick better.