This very interesting thread has exemplified some severe-duty successful applications of JB Weld.
I can't compete, so I will go in the opposite direction.
I have a (supposedly) high quality fly reel from an old high-end manufacturer with some hairline cracks on the back (frame side), both inside and out. As I have read it, the cause was too much pressure from die stamping in the manufacturer name and logo on the back. I can't tell if the cracks are just on the surfaces, or full thickness.
The reel is long out of warranty, unlike for example Orvis fly reels which come with a lifetime warranty against factory defects.
The reel has only seen light use, so as far as I can tell, there has been no issue besides their presence. But I didn't like it. Having no other alternative I opted to (probably) go overboard with a fix.
I bought a couple of small flat stock steel angles at the hardware store. I mixed up some JB Weld, coated the contact side of each angle, and pressed each on to the inside surface of the frame. Pressing caused some of the JB Weld to emerge from underneath the angles, but still in contact with the aluminum frame.
It took what I thought was a long time to cure, having a plastic feel to the surface, but it was a thick coat. I just put it aside for a few days, and when I next checked it, it was extremely hard. Between the direct presence of the JB Weld and the splinting effect of the now-integral steel angle stock, I think I have more than sufficiently reinforced the frame.
The best part is this fix does not affect function and is not visible from the outside. The spool has to be removed to see it.
Overkill?
I hope so.