Hi all. Changed my gearbox/ transferbox and rear diff oil today. Has anyone else done this themselves? The gearbox/trannybox oil came out a clearish yellow colour, but the rear diff oil was nearly black. Guessing i have an issue going on in the diff somewhere? Refilled it with OEm fluid (75/90 i think) which was a lovely red colour... Which has made gearchanges less crunchy and no whine on over run now. Any idea why the diff oil could be so dark?