The bearing is there in ensure electrical contact.
My Gladius (1st gen ceramic) won't budge, at all. No chance I will ever try to get it open.
My friend's Gladius (HAIII, with pretty bad texture differences between head and body) unscrewed just fine, OTOH. There was a little glue on the threads, but not much. The reflector and electronics are larger than the ID of the body. The light cannot be assembled from the back. The electronics and reflector are mounted on a plastic tube (you see the end of it at the end of the light when you unscrew the tailcap). It has three flexible flat cables on the outside (for the three modes). The ball bearing is part of the alignment, but also provides contact. My friend got some silicone lube on it, with weird and nasty effects on performance.
Frankly, it looked a little fragile when taken apart. My advice: Don't touch it, unless you really, really, really want the mod.