Rendezvous LSD Clutch Panel Check Valve Assembly

[ceecee2_]

I have a 2006 Rendezvous that the AWD disabled light has come on. Right after that when the transmission was trying to go into overdrive the RPM jumped way high.
I took it to the shop and they diagnosed it as needing "Limited Slip Differential Clutch Panel Check Valve Assembly" stating the diagnositics showed the sensor shorted out.
I have an extended warranty through a third party....non GM warranty.
The GM dealer stated I needed the Limited Slip Differential clutch panel check valve assembly.
My question is, is this considered an internal lubricated part within the drive transaxle assembly.
What does the sensor do? The AWD is not working and they changed the fluid again......this was done less than 5000 miles ago.