I would call their 800 number or email them. That number is 800-879-4868 M-F 8am - 4pm EST. or email at email@example.com. There is a 10y limited warranty (original owner) so you may get the part or a new one at no cost depending on your situation.
I'm assuming a "smart stop" feature would be the motor stops when the pencil is sharpened. This sharpener stops sharpening but the motor will continue if a pencil is inserted, it just doesn't keep grinding the pencil tip. You hear it being done.
Why would you spend $23 for a cutter assembly when a new unit is between $25 and $29?????? So yes you can but I think it is a bad investment. I'd much rather purchase the Teacher Pro which is a better model...and although you can't replace the cutter in the Teacher Pro it is about the same price at the School Pro.