I've used a couple of AFV Club U.S.track sets and definitely had problems with the loose end connectors. On my first attempt at correcting that I brushed Mr. Surfacer 500 on the pins to bulk them up a bit. Had to do put a couple of coats on. When dry the end connectors did stay on, but I think the lacquer base on the Mr. Surfacer weakened the tiny pins and they eventually started breaking, but it was months later.
Then I read on these very forums a neat trick! Use a sharp needlenose pliers and pinch the middle of the pins just enough to make them "bulge' a bit. Just enough to get those pesky end connectors to hold on. I tried that on my next set and it worked like a charm! I lost a few links due to overpinching, which made it difficult to press the end connectors on and resulted in some broken pins...ooops!
Anyway, here are some photos:
This is the 2nd set I did, T48 Sherman tracks. Basically the same setup as the T80 and most U.S. links with end connectors. I used the pinching method on these links. As you can see they fit pretty good and even with some pressure to get them tight they didn't break nor did any of the end connectors slip off.
Steps to alter the pins. First: this is one of those T48 links:
Next pinch or squeeze just the middle of the pin using needlenose pliers or some strong tweezers
If you squeeze too hard you'll get something like this!! Actually I did that on purpose so you can see it clearly in the photo. The first couple I did you could barely see the bulge in the photo. I have to stress that you need to be careful and not overdo the pinching, otherwise you may ruin too many links. Fortunately these set usually have enough extra links!
See...they hold on pretty good!!
That's it! Do the same to all 4 pins, multiplied by...what 160 or so!! Yeah, its tedious, but at least you won't have to throw that AFV track set away.
The only other tip I have is if you're going to do a wash on the painted tracks don't use enamel thinner or mineral spirits. Those liquids are hot enough to eventually weaken those pins and then you have a disaster! I would base paint them thoroughly with acrylic paint, then overcoat with enamel paint, then apply a water or alcohol based wash.
Or you could just get some DS tracks!!
Hope this helps!