I recently had an issue with my SS All-Wheel-Drive @ 62k miles. While I don't have a decoupling spline in the bearing housing, I think the issue is the same. The primary failure mode was lack of spline lubrication. I've attached some images of the failure.
I'm shocked that GM decided to use grease to try to lubricate involute, high speed, working splines. Splines used in this type of application need an oil bath...not grease. Grease is for low speed splines or non-working splines. I've never seen grease successfully used on high speed working splines. The closest application to this is the slip yoke found in some drive axles...and those are typically square tooth splines with a special plastic wear coating.
The pictures below show the bearing assembly damage, a closeup of the lack of intermediate shaft engagement, the intermediate shaft spline damage, and the lack of lubricant on the cv drive axle splines. Hopefully, I'll have a permanent fix in a few weeks...I don't want to pull this apart to grease it every year.
When I'm done...I'll post the results.
When you get the new parts, you will want to take some additional maintenance actions to keep it together. Your component degridation won't be as fast as my SS because you are all-wheel-drive all the time...but it will happen again.