I have the 2021 version (son does), MXZ Sport 600EFI. Put about 800 miles on it. Runs very well, starts good, efficient and will go about 80.......Not sure what you are getting at about a potential rebuild, but variations of these have been in the Ski Doo family forever. I had older EFI sleds, then evolved to SDI then Etec, and have had literally ZERO problems with any of them. Not a motor head, but assume engine has been somewhat redesgned and upgraded with modern and functional parts. To me, good value snowmobile.