E30 Zone

I've just drained the differential off my 325i and wondered if it's worth flushing it out with a cleaner? If so, what would be an ideal product to use? Any recommendation on the replacement oil would also be handy.

Don't know about flushing, didn't do it myself...Is it really necessary? The old fluid looked like new in mine.

Anyway, 75w90 (Fuchs Sintopoid) for open diffs and 75w140 (I used Castrol Syntrax), if you have an LSD.

Roughly 1 ltr for small case diffs and 1.7 ltr for the larger diffs. Fill up until it starts to pour out and then put the plug back in. Would be useful to put some plumbers tape on the plug, as mine kept pissing oil until I sealed it.

Source > http://www.e30zone.net/e30zonewiki/index.php/Oil

The flushing was just an idea. If it's not necessary I won't go down that route. Will just fit new axel seals, plate gasket and top up with new oil. Thanks for the pointer.

Oil drained from a diff. should always look new, but that doesn't mean it is. The long chain molecules that give an oil its viscosity eventually get chopped by continuously going through the gears.
If the drained oil doesn't look new, then you have serious mechanical problems with the diff.
The small amount of oil left after draining will mix in with the new and will be insignificant.

My drained oil was black and smooth which had me wondering how old it was. I can't imagine the last owner had ever changed it but at least it wasn't brown or anything nasty looking.