I want to drain and replace my rear differential fluid on my BMW 650 XDrive, from my research BMW uses Hypoid Axle Oil G1 (BOT448) P/N: 83 22 2 295 532 which is a 75W85 GL-4 oil, I want to try out the Redline 75W85 oil, however, it is a GL-5 oil, even tho on the redline website it says it is compatible with the BMW 75W85 GL-4 oil even included the BMW part number, from more research online, some say that one should not be using GL-5 oil in GL-4 car because it has sulfur which could cause wear, experts please do chime in. As well is Redline oil a superior product compared to BMW gear oil? or are there other suggestions and why?