I can't seem to find much on this that answers my question, not in my service manual either.
I can see my rear differential has been leaking at the cover. Does anyone know what the seal is made of? Is it a specific seal you have to puchase to replace or is it just black RTV? I'd like to get a better idea before I pull it off.

 

Go over to Autozone and buy a gasket. It's $4.99 and it's a Fel-Pro.

The factory uses RTV.

 

Thanks,
I was under the impression that I would need to use an additive as I have a Trac-Loc rear, but my owners manual does not specify that. It only mentions the additive for the 10.25" axle, not my 9.75". Thoughts?

 

All Ford LSD's need the additive - and 85W140 full synthetic lube.

 

Yeah I ended up rereading the manual and in the note, they have it seperate from the rest of the note. 4oz. And it's 75W140, not 85. Thanks.

 

Oops - sorry about that - DUH!

 

If you decide to just use the silicone for a gasket, you must make sure the surface is clean and dry. This is difficult because there is usually some lubricant slowly running out. If there is any fluid on the gasket surface, you will have a leak when you finish. Since the synthetic fluid and additive is very expensive, you don't want to do this over again.

Also, when I drained mine in the 2000 because the traction lok was chattering on corners, I replaced the fluid and modifier and the traction lok still chattered. Then I found out about the TSB that recommended in this situation to replace the trac lok clutch plates and remove 0.010" preload shims. The parts guy at the dealer said most people just add another bottle of friction modifier and that takes care of the problem. That is what I did and it worked. 65k miles have been put on the truck since then with no problems.