One of the 2 local WMs close to me only had 2 quarts of the ST syn 75W-90 gear oil in stock for my 06 Tacoma rear differential, I bought them thinking I could grab another one from the other WM just down the road. Didn't work out for me, as the second store had zero in stock even though the website said they had 15. My brother has a full quart of Amsoil 75W-90 that I can use, my question is can I mix the 2 different gear oils without any problems?