The XL motor endcaps are pressed in and it does look like there is some sort of adhesive as a supplement. However, this is a common issue and is solved by using the RC-Monster heatsink/clamp. Just choose the XL version...
I had an endbell come off a HAcker motor and was told to use green loctite to rebond it.Worked great and it's still solid after many hard cycles.It's important to get the endbell mostly in place and then wick in some green loctite just before snapping it closed.Wait too long and you may have a problem getting it to seat properly if the glue goes off too quickly