The dealer apparently SELLS the nut and O-ring as one piece. They don't sell the O-ring by itself, or at least it's not listed in realoem as an individual part. My error in post #8. But you can discover in realoem that the O-ring size is M22X1.5 - see post #3. Then your choice is go and get the O-ring somewhere else (Oz equivalent of McMaster-Carr here), or shell out whatever the dealer wants for a couple of plugs-with-O-ring.

You're making way too big of a job out of this (unless you're just trying to run up your post count for some reason - nobody else had 8 live threads on page 1). More time has been spent on this thread than it takes to change the differential oil.

 

OP - You're going to waste your time and money changing the differential oil in this car. Up to you. This is one of the only things I agree with BMW on. I have 400,000 + miles on my E39 2000 and never changed differential oil. I changed in my old 99 E46 when it had 130K or so on the clock and it looked good. I almost reused it.

 

Considering that you have noticed the time I spent on the forum, then it is all thanks to my beloved E60 which I like to keep instead of selling it cause there are no good Indy's and BMW guidance for maintenance is up its back entrance. I have got issues with my car starting from most common ones like engine oil leaks to most bizare and rare ones to Trans electrical one.

Plus, when I come for a totally non mechanical background, and realised what I had bought i.e. E60 then every single nut and O-ring makes the difference as I don't like to keep fixing the leaks but do it right the first time.

So thanks for your input so far.

 

Since I did the diff oil change last week, my suggestion to you is to change it. After 135K, the oil that came out was black and there was a lot of sludge or crap at the bottom of the differential. I have not heard too many issues on the Diff due to oil, but considering all the other problems I am facing, I just thought to go ahead and do this change and glad that I did.