Thermostat install?

I am taking apart the upper and lower to figure out where the coolant leak is coming from. When I took the water neck off the termostat fell right out. I was reading in the my book that some T-stats have locking ears that you turn to lock it in place and the some have a spring like flange that holds it in place. Mine has niether, not does it have a bleeder hole and I don't see anything in or on the lower and water neck that would hold it there, just an inset on the water neck. Since I have a GT-40 lower is that gone now, or how does it lock into place, especially to re-install it? It looks like the old one was RTVed up to stay but has since came free.

Also does the spring side of the T-stat go into the lower or the other side. it fell out so fast I did get to see how it was oriented.

Thanks and sorry for the trivial question.

Thanks for the help!

I hate RTVing stuff up just doesn't make sense that there is not a way to lock or hold it in place.

Any other suggestion anyone!