Re: replacing rear extension housing.
do this with the rear of the car Jacked and BLocked (on car stands) as high as you can get it.
Simply remove the tail shaft, speedo drive and Crossmember (support the box with your trolley jack)
Being a 6 pot, the exhaust shouldn't be too much of an issue. The Exhaust mount and gearbox mount can be changed once you have the extension housing off.
By jacking the rear of the vehicle ONLY most of the fluid will run to the front of the box, and you will have minimal fluid loss. (last one i did, the loss did not register on the dipstick!
The secret to this job, and it is EXTREMELY important, is cleanliness. The clean the surfaces for the gasket, the less chance of a leak. And MORE importantly, autos do NOT like dirt at ALL. one speck of dust is enough to upset the valve body.