According to Ebeneezer Geezer :
I wonder if something like JBWeld would work or whether I'd have the same
non-sticking issue?

Which "non-sticking" issue? My comment was regarding trying to solder
galvanized (or otherwise soft solderable) sheet metal to galvanized gutter.
In order to do that, you have to remove the paint from the gutter and
clean the galvanized sufficiently to be able to solder to it. It's my
belief that by the time you've cleaned it that well, you've scratched
off enough zinc that you'll have bare steel spots. The solder will still stick
(to the remnants of the zinc), but there will be so much bare steel (where
the solder won't stick) that you won't get a waterproof patch. Besides, the steel
will now rust.

You could silver solder/braze a patch, but, frankly, I doubt that
many people could accomplish a satisfactory patch that way ...

Seems a shame (no make that incomprehensible) that there is not some way to
patch an eavestrough.... we need to bring the entire intellect of the known
world to bear on this issue....(please..LOL)

I'm certain that epoxy, bondo or JBWeld can do it. Clean it thoroughly, avoid
coarse abrasives (so you don't expose bare steel if you can help it), and make sure that
all bare metal is covered by the glue. To "span" the hole (support the epoxy
over the hole), you could use some aluminum sheet or even window screen scraps.

It's better if the glue is moderately thick, or it'll just run off (ie:
straight West Systems epoxy is almost water-thin). So you may need to use a
thickener if the glue is thin. Fine sawdust will "do" if you have nothing
better.

Commercially, gutter installers use some sort of asphalt-like caulk (to seal
joints). Even ordinary (preferably silicone) caulk would work if the holes
were small and it had time to cure properly.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.