This has always been a weak spot with the FX series. I can't even begin to count how many times I've broken that mount off. In the later engines OS has corrected this with a metal mount that is bolted in place, but on the FX if you hit the ground you can bet good money that mount is going to break. Over the years I've tried everthing I could think of to repair the broken part. Trust me when I say that nothing really works very well. The closest that I've found it JB Weld, but it won't hold very well. The vibrations and the lack of a good surface to do the repair with will cause it simply come back off. And it usually doesn't take long before it comes back off. It's not worth the effort to try and repair it.

Your best bet is to simply buy a new back plate. You can get them from Tower Hobbies for $9.99. I usually order 2 or 3 of them just so that I have one on hand for future repairs. Here's the part you need:

[link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCG04&P=ML[/link]

Ken