Not sure of the year of your outboard, even so, it looks like a simple
remove and replace to me. As long as you kept up with your lubrication schedule.
Looks to be part 17 of the linked diagram. Check the year though before ordering parts.
http://www.boats.net/parts/search/Yamaha/Outboard/2006%20and%20Later%202-stroke/25MLH/BRACKET%202/parts.html