If you're OCD like me and it bothers you that the cover in the reinforcement plate (where you access your oil drain plug) is missing, even though your dealer will tell you they are NLA, you can still get one to fit. It's not really missing, they just stopped installing them at some point. Part numbers are: 51617199687 for the cover and screw and 07146981767 for the c-clip. These parts are listed as being for a Z4 actually. It should work for both coupes and sedans since they both use the same reinforcement plate.
http://www.realoem.com/bmw/showparts...51&fg=80&hl=13
I installed one on mine a while back so I can confirm this is the right one. Cost about $6. I sleep so much better at night knowing this cover is there.
Barry