Mercruiser raw-water heebeejeebees

[Rhodnett]

My '74 SF 23 has a '93 5.7l Mercruiser raw water cooled with 730 hrs. I bought the boat from a friend last year, and I don't know how often or if it was flushed after use. During the course of having the oil pan replaced (rusted around the drain plug), the risers had to be replaced....the ends where the hoses attach were rusted and falling off. Other than that, everything looked OK...(as far as we could see, that is).