See my thread here http://www.e90post.com/forums/showthread.php?t=639210
I have changed mine in the past, I would always reccomend changing the seals first rather than the pipe it self as its expensive.
From memory it is the rubber seals that were modified to make it a tighter fit but from 09 onwards they changed the design of the pipe as well.
IMO something like this I would always reccomend to use genuine part plus I do not think there is aftermarket pipe available unless if you are willing to get creative blue peter style
This is DIY possible if you are handy with spanners as the top airbox comes off, bottom under tray comes off and accessiable.
One thing I would urge for you to look/change is the oil breather pipe as this is possibility one cause for oil pressure build up and leaking around the seals.
Mine was not covered under BMW extended warranty so pretty much doubt WD will cover it but nevertheless see what they say.
The 2 seals are about £9 each and should not take more than 1 hour labour charge. New pipe is about £165