It's time to change the oil in the front and rear differentials on my Subaru Legacy and I can't decide between Valvoline and Pennzoil 75w90. I plan on getting their full synthetic. I'm expecting to be told "it doesn't make a difference" but wanted to make sure and see what kind of input I'd get. Car in question is an automatic, so no concern over what kind of impact the oil has on shifting since the AT and front diff don't share the fluid. Thanks guys!