Some ARF manufacturers actually use loctite on their hardware. If it is blue loctite, a little heat from a soldering iron should do the trick. Assuming that the engine mount is metal, yes, you should use blue loctite to re-assemble.

Wow, I typed up that whole answer without looking at the pictures. When I clicked on them I got really scared and was about to ask where was the other half of your engine mount. Then I saw that your engine mount actually supports the front of the engine with a 3rd member. weird, but it works.

Rafael