If your son runs his motor a lot he needs to check
for this O ring. Its a seal for this end of the drive
shaft. If it has never been checked its probably
dried up and disaggregated long ago. Replacing it
among with a light coat of lubrication can avoid
this from happening.
Tubs.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.