My mechanic says I have a cracked extension housing which is causing my 2001 Jeep GC Laredo to leave a lake of trans fluid in my driveway. He says they do not make the part any more but he cannot give me a part number or anything. He says it is in between the transmission and transfer case. What part could he be talking about?

 

From your description, it is the underdrive housing/front half of the transfer case. As far as buying one new I don't know. But if your mechanic is doing the work, you would be money ahead fo get a used tcase and have him install that instead of tearing apart the whole tcase and reassembling.