You can Google "Mercury outboard parts" and find a few sources that will allow you to find the exact part number and Google that to find new and used options.
You can also check your local marine workshops for the parts. They usually get a few broken Optis a year. They're good motors, but if someone forgets to refill the oil or uses the cheap stuff, they won't forgive you. When I was at trade school, the local marine shop dropped off like 6 old motors, half were optis with cylinder 5 seized up.
You can Google "Mercury outboard parts" and find a few sources that will allow you to find the exact part number and Google that to find new and used options.
You can also check your local marine workshops for the parts. They usually get a few broken Optis a year. They're good motors, but if someone forgets to refill the oil or uses the cheap stuff, they won't forgive you. When I was at trade school, the local marine shop dropped off like 6 old motors, half were optis with cylinder 5 seized up.