You still haven't described anything we don't see here in the northern U.S. Every day. I've seen the huge rust flakes I think you're seeing, and it is almost unheard of to have a leak be the result. To prove it to yourself, tap on it with a hammer. There's no pressure on the housing when it's in operation so if the hammer doesn't cause a leak or even dent it, driving it won't either.
After thinking about it a while, there are two different styles of differential housings. Some have a stamped steel cover that is relatively thin but even those rarely leak. I've never replaced one. I think your truck has a solid housing and the differential assembly drops out toward the drive shaft once that is unbolted. If that's what you have, you can definitely stop worrying about that rust. That steel is over 1/8" thick and will never rust through. I have a couple of those axles here from cars that were driven in salt for over 30 years. They're ALL rust and scale from top to bottom, ... But they don't leak.
Gee, it's nice to give good news for a change!
Thursday, February 7th, 2013 AT 5:50 AM