I had the issue of the lid not closing all the way too, but I caught it before I ran the truggy, because when I carried it outside from where I fueled it at, I leaked fuel down my leg....talk about sucky.
Anyway, I have made it habit to push down on my lid too. I am not sure what the deal is with this, but I am gonna get some new fuel line sometime, another new glow plug, and sometime down the road, a new fuel tank. Everything seems to be good, so I figure I will do little inexpensive things for right now and see what happens.