List For a 65 3000 Sunday driver should I use Valvoline 85w-140 or Castrol Hypoy C 80w-90 in the Diff? Does it matter? I have the Valvoline in there now. If the lower visc Castrol is OK, will I cause damage if I mix the two? No! I haven't yet. The diff oil level is pretty much where I left it last year, but I am interested in changing it. TIA Greg Sent from my iPhone.