I've had my M2 since early 2013, though it was put away for a couple moves. I recently got it back out, did the upgrade to 24V and V4, and it's working well. During a few test prints, I heard a cracking noise, and started noticing a bobbing of the extruder. It turns out that the extruder motor mount was cracked (maybe I over-tightened it). Even bobbing a little, it was printing pretty well, and I found an upgraded version in the GitHub, so it's good as new now.
I considered this a warning, and printed spares of all the parts I might eventually need. I just can't get over how cool it is to be able to do that

Thanks Makergear!
Rusty