I’ve never changed the differential fluid in my 2015 Forester (85k) and figured it’s about time. I went to pick up three quarts of Diff fluid at the local auto parts store. They had a great sale on Valvoline 75w-90, but only had two of them. They had Mobil 1 75w-90 for a few dollars more. I bought the two Valvolines and one Mobil 1. The diffs call for about 2 quarts total, though I’ve seen write ups that say as high as 2.2 quarts. I figured I could put the Valvoline in and top off with the Mobil 1 if necessary. That should be fine, right? We’re talking maybe 1/10 to 1/5 of a quart of Mobil 1. They’re both full synthetic, same weight. I should be able to sleep at night for the next 30-50k, yeah?