X5 4.4 - Sludge in engine and oil filter housing... help!

[FSETH]

sunny, Are you a BMWCCA member? If so, I HIGHLY suggest e-mailing tech-talk and getting a copy of their old school maintenance schedule. It is written by Mike Miller who is more than likely a better BMW mechanic than your guy seeing as he does the mechanical questions for both Roundel and Bimmer magazine. In the maintenance schedule, he flat out states that it is risky to drain a previously unmaintained automatic transmission with higher mileage. Pretty much stating what everyone else here is trying to tell you that he has personally seen TOO MANY properly functioning automatic transmissions go shortly after a filter and fluid change. Shifting of sludge is just one of the reasons he states it can happen.

and like JCL pointed out, he goes on to say that he has seen properly maintained transmissions break anyway and that there is just no predictiing them. He says he has seen un-maintained as well as properly maintained units both go 200k. Unfortunately, I can't post this PDF from the CCA as they ask you not to, but you can obtain a copy with your $20 membership. There is over a page dedicated to automatic transmission maintenance. Maybe you could print it out and take it to your mechanic?

Pretty much like we all have said in this thread. There is no right answer when it comes to changing the trans fluid and you should do what makes you happy, but calling the risk of changing fluid on a higher mileage BMW that has not been maintained an urban myth, is just flat out inaccurate.