It is worth investigating whether you actually need a new transfer case. Many have repaired theirs with a new front driveshaft output yoke. Racemalibu (a member here) was providing them, not sure if he still is. It would be a lot cheaper than replacing the transfer case. Also, reposition the AC drain so that it doesn't drip on the driveshaft in the future and contribute to the corrosion issues in the coupling.

Do a search on front driveshaft or racemalibu for all the details.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue