kghost, I don't think the latch can be TIG welded, as it is not made of metal, but some kind of hard plastic that resembles metal (I don't know the english word for it). I'll try to "loctite" it or "jbweld" it, but as you can see in the pic, the contact surface is tiny and there is almost no place to use a reinforcemente. Probably I will use my dremel to drill a tiny hole through and will use a pin as reinforcement. Anyway, I'll come back with the result.
Removing the rivet was not that hard. I only was very careful to avoid the drill skipping and causing a catastrophe to my tank. I didn't want to drill too much either, so the hole in the tank was not enlarged. After eating up the biggest part of the rivet, I used one of those punches that are used to hide the heads of nails in wood, that are straight and hard. A couple of knocks with a plastic mallet and that was it.
Raul