The first would be for replacement of the shredding disk (flywheel) and shredding ring. This normally is needed only after years of hard service. Second, it may be necessary to replace the scab Always do this when replacing the shredding ring. High-quality neoprene seals in modern disposers last for years and normally good for the life of the appliance. Finally, in case of motor failure, I the disposer would have to be removed from the sink and the housing assembly would have to be removed. Accompanying photograph show you how. But be forewarned that on many older disposers housings were sealed and are not serviceable. For the most part disposers were covered with long-term warranties.
Check Cypress Appliance Repair for disposer grounding after reassembling. There is easy way to make an unjamming tool for those hard-to-budge jams. Grind or cut a notch in the end of the stock to fit the ear into the hole slightly larger than the flywheel nut as indicated. Finally, insert the L-shaped unplug the disposer and insert it so that the nut is within the hole of the mid the ear is in the notch. Now, with a crescent or other suitable wrench which can easily apply be to the disk to loosen all but the most stubborn jams.