Just had mine done last week. You can read about it in one of the threads.
The pinion seal has been replaced by GM with a kit that went to dealers a couple of months ago. I read that on the board. The new kit will be installed under the pinion seal leak recall happening in February.
You and I should have the new pinion seal, which is GM's fix for the leak. Other vehicles will be outfitted under the recall. I wouldn't worry about your new differential anymore than any other car you've owned.