It is the paper feed mechanism that seems to fail for me. One machine which I'm about to swap out still faxes fine yet won't copy. I'm envious because I'm sure you probably do not have the 20 ream a month (10,000 page) habit my practice has.
I have an MFC 8670DN and so far ok after a year yet a little tricky with the paper feed from the tray (can't load too many sheets in or it won't feed.) The Brothers are so easy to work and my staff and I really like them, yet under heavy use I've seen only average reliability. (My home machine is going along great at 2 1/2 years yet it is still well under 5000 pages).
Thanks for the feedback.