To rebuild or not to rebuild...that is the question

sounds to me something else caused you to lean out wether it be a cracked throttle body boot, leaking crank seal or a plugged injector, even a kinked fuel filter line could lean it out if you were running one of SPI's filters. I would pull the motor fully and do a complete tear down to find the culprit. Order a complete gasket and seal kit, send your injectors out to have flow tested and cleaned, new pistons and rings, Deglaze cylinders considering the piston didn't wipe the cyclinder after it melted and if so then you would have to consider buying another cylinder, new throttle body boots. While you are this far you might as well check the motor mounts and replace them if they are cracked. Depending how much you love your 900 is going to be the factor to rebuild or not to rebuild. I love mine and will probably never get rid of it. Hard to find a machine out there that Torques like these machines.