I've owned, modded, worked on, and maintained both N54s and N55s. The lack of reliability with N54s is WAY overblown in my opinion and candidly prefer N54s more due to how strong they are out of the factory. I've had two DD N54s now (one was FBO and the other completely stock), both of which were as reliable as anything I've ever owned.
Speaking of clean 335xi's for sale, check out the link to the one I have for sale now.
https://www.e90post.com/forums/showthread.php?t=1529842