Changing diff fluid

i've read somewhere that Ford switched over to 75w 140 in '01 but i'm not sure. RTV or gasket maker is a silicone sealer that's in a little tube, personally i think makes a better seal than just a gasket

Take a look at the following web page: http://www.weather-check.com/royal_purple.htm

RTV is the only way to go. RTV=Room Temperature Vulcanizer

You use RTV to spread on the surface of the differential cover and the edge of the differential to make a good seal.

When you change the fluid, scrape all the funk off the cover/diff and then spray down the diff cover with brake parts cleaner/carb cleaner to clean it, wipe it down. Take a old t-shirt or another lint free rag and wipe down the inside of the differential. Before you apply the RTV, make sure that the mating surfaces are clean. Spread it over the bolt holes, put the cover back on, tighten bolts, done.

Not difficult at all. Just messy!! Get lots of paper towels and newspaper.