Can water get up to the air intake??

[Kettlewell]

Hmmm--the exhaust elbow doesn't necessarily need a siphon break if it is located far enough above the waterline, but in your case you say it isn't. Here's another good article on the subject. I hate these things where the boat is set up in the first place for eventual failure once something goes wrong. As long as that seacock was closed after each engine use you probably wouldn't have had a problem, but someone expecting that to always happen was very optimistic.