Hi:

I just installed a good used Engine in my turbo wagon. I did all the things the first two posts mentioned. Especially the rear Main seal and Oil Pan Gasket. If these two leak while in the car, you have alot of work on your hands. It's a piece of cake when the engine is out. Front seals, Timing Belt and Water Pump can be done in the car. But still easier to do when the Engine is out. Also check your Turbo, if equiped, it's much easier to change out of the car. There are two Cap screws for the Oil Return Line and a nut on the bottom of the Exhaust Manfold that have to come off before the Turbo and Exhaust Manifold comes off (Garrett equipped). You have to lay on your back under he car to get at these. I found this out the hard way. Finally, if you have an Automatic Tranny, you should change the Front Seal.

Good luck
Warren