does the seal between the two truly seal the fluid or is it shared fluid between them.

My mechanic says it is shared.

If it isn't shared that may explain my irratic reading when trying to check the trani fluid.

does anybody have the seal number so I can get the correct seal between the trani and the transfer case it is oem only or can I get it at napa.

 

Your mechanic is mistaken, the fluid is not shared. There is an input shaft seal on the transfer case, and a gasket between the transmission and the adapter, and another gasket between the adapter and the transfer case. All are available at a GM dealer. Some guys use RTV instead of the gaskets, but from the factory it had gaskets. If the seal leaks, the fluid level in the transfer case will rise, and the level will fall in the transmission. Quick easy check is remove the fill plug on the rear of the transfer case, if fluid runs out, the seal is leaking.

If the fluid level in the transfer case rises to the vacuum switch, and if the vacuum switch is faulty, it can suck fluid into the HVAC & 4WD vacuum systems.