I don't know if this problem is more prevalent on the 5 series, but it is certainly a lot more talked about on the 5er forums.
There have been many reports of ingested flaps, of earlier and later types - although, to be fair, there are a lot less instances of failure of the later type enclosed, with larger spindles.
I spent a couple of happy hours removing mine from my E60 530d, which gave me some peace of mind as the car is out of warranty. I even got a little better fuel economy afterwards too - bonus!
I'm looking for a 335d now, and I will certainly be throwing away the flaps on that when it comes out of warranty. Maybe this time I will go for the machined blanks, rather than re-using the flap bodies and a screw to block the hole.
Question: Do the E9x series have proiblems with engine breather filters, like the 5 series does? An easy, if time consuming, job to do and relatively cheap - this is now an (undocumented) service item for the 5-er. Every 3 oil services it gets changed. The original problem was that the early filter was a plastic mesh which got clogged and pressurised the engine oil out! The later filter (interchangeable) is a "vortex" type that can't block up.