Just changed my oil on my '05 545i yesterday. Thanks to all the DIY posts on this forum for making it an easy job! I also had the issue of not being able to loosen the drain plug out of the filter housing. I believe i read some where to simply use a 24mm wrench to hold the filter housing in place while you loosen the drain plug. I only had a 24mm socket available, so I couldn't hold the housing and I didn't want to risk using an adjustable.

The car seems to be running MUCH more smoothly and feels like she even has a little more pull. Maybe it's just psychological?

 

In case you don't have a full mm set, a 15/16" box end wrench or socket fits the 24mm housing nut perfectly and will not round over the plastic nut. 15/16" is 23.8mm, and actually fits better than a 24mm on the housing. Either six or twelve point will work.