Rubber Boot on Swingarm/Final Drive

[JC-RT]

Back in October I greased the final drive splines on the final drive on my 2015 RT.  Test rode then and realized that the rubber boot was not staying in place. It was coming loose.  I took it apart again thinking that I had reassembled something wrong. After reassembling  and rotating the plastic piece within the rubber boot to make sure it was connecting well at the tabs. I put about 100 miles or so on it without any problem.  Then last week I went for a 50 mile ride and realized today that the rubber boot had popped loose again. It is coming loose at the "front" of the boot where it connects to the swing arm (drive shaft housing). 

Any ideas on what I am doing wrong?
I have turned wrenches on many a Japanese and US motorcycles and cars so am not a newbie to mechanics, however, this is my first BMW motorcycle and realize that I might just be missing something.

[Beagle]

Looks like there are tabs to locate but is it possible its swelled with oil or grease contamination.

[simbo]

Rubber deteriorates over time, is it time for a new (more flexible) boot?

[Beagle]

It may be you could clean the boot and housing surfaces with Isopropyl alcohol or similar and use a suitable glue to keep it in place.

[David.]

[JC-RT]

Thanks for the replies. Yes, this is the part in question.

In the picture it looks like the rubber boot and the plastic are adhered as one piece. On the one currently on my RT the plastic piece moves independently of the boot, but the larger flange on the plastic piece keeps the boot from moving away from it thus keeping the boot from separating from the plastic .  Is this normal?