I think so. Running Difflock oils in Gbox and Tbox, but not diffs. A bit smoother, perhaps, but not a huge difference. But also bear in mind that Difflock say they last twice as long (You are a fellow Yorkshire ex-pat, right?) and give better protection etc, so worth doing I reckon
I didn't go for Difflock in the diffs. Sticking to standard stuff and changing more frequently in case they get water contaminated - Not that I do a lot of deep wading in the Td5, but diffs are a piece of cake to change too.