I have a 79 F-150 4x4, 460, C6 and NP205 xfer case. I recently had the C6 rebuilt and have been using the truck for about 2 weeks. I just noticed a whiing, clunking sound coming from the transmission or xfer case. I have noticed a oil leak in the xfer case and have added gear oil. This doesnt seem to help. My question is where do I start with troubleshooting? It very hard to determine where the noise is coming from while your driving the truck. If it is the transfer case how much can it cost to get the xfer case rebuilt? How hard would it be to overhaul the xfer case myself? Any help appreciated!!:-(