Here is the final drive (differential) as it was removed from the donor Sierra rear beam. Quite sorry looking, with some oil on the case where the original oil seals had started to fail.
First job was to remove the nut on the prop shaft flange. Then the flange itself could be removed with a three legged bearing puller. The three oil seals were removed by pulling very hard with adjustable grips, being careful not to damage the inner surface of the final drive unit.
After spraying with water soluble degreaser the final drive unit was steam cleaned using a domestic steam cleaner and a small wire brush drill attachment. The result was very good, with all oil and dirt removed. During the cleaning the openings were covered to prevent debris, degreaser or water getting into the internals. A couple of coats of Hammerite special metals primer were added. This ensured the silver top coat would have good adhesion.
The final drive unit was then given two coats of smooth silver Hammerite. The prop shaft flange as well as the nuts on the rear of the unit were painted in black Hammerite. Then the new oils seals were installed, using a suitable drift and hammer. Camberley Auto Factors no longer stock oil seals or other parts for the Sierra, but eBay came to my rescue (yet again).
Here is the final drive mounted in the chassis using the new bolts and nyloc nuts provided by Tiger.