This is a great thread. I'll be replacing the front diff fluid on my 35i at 36.5K miles because I was really dumb and ended up draining my front diff when attempting to change the engine oil today. I knew I was expecting a 17 mm drain plug but grabbed my 14 mm allen and proceeded to crack it loose and open her up... I smelled it as soon as it started flowing but I dropped the drain plug into my oil drain pan and about 5 seconds later it was all out. It was pretty dirty so I'm not too mad.
I do have some Redline 75w90 GL 5 that I incorrectly bought for my E46's rear diff last time I changed it that I'm going to pump into it temporarily while I wait for the right stuff so I can drive it.
I guess a bonus is that I noticed an oil leak around a hard line going into the turbo and dripping down on to my passenger side axle shaft and belly pan so yay?