A reputable radiator shop should be able to clean it. I took my heat exchanger to a radiator shop for cleaning, and to repair a few leaking tubes. Unfortunately, the tubes had deteriorated to the point where they needed replacing, so there was no point in cleaning the heat exchanger. I replaced the whole unit.
Which leads to a question, Ted. Does your boat have a 2" or a 3" diameter heat exchanger? If you have a 2" model and you end up needing to replace it, you may want to change to a 3". You can find a lot of info on this site about heat exchangers and overheating problems in general.
