Re: Diff oil of choice
Are synthetics in differentials really needed? It's not an engine, rather just a bunch of gears with teeth. Normal gear oil is pretty tough stuff. That said, Amsoil sythetic extreme 75W-140 in mine.
The main advantage I can think of is a longer service interval but I sort of want to stick my nose in there every 20,000 miles anyway and see how the oil looks.
2005 E350 RB 6.0 PSD for extended fun
1989 Landcruiser FJ62 for local fun
2011 VW TDI Golf for hwy fun