I think i have found the best diff fill you can buy. It is high-temp gasket sealer from an autoparts store. When it dries it is a stiff liquid like silicone, but it is very sticky. It makes the inside tires slide a bit on wet street and things, But it still lets the diff work unlike glue. And if you need to remove it, it instantly disolves in acetone. I now have limited slip diffs in my MP that can be changed back to stock, and the sealant doesnt leak out like silicone oil. Only problem is it makes getting them back together after you fill them hard because it gets in the screw holes of the MP diff.