Thanks for the reply. I agree that flushing the coolant side is not needed if you change as often as you do. You can't go wrong following what the manufacturer suggests, so I totally understand why you are following this routine. Running in freshwater most of the time should GREATLY reduce the build up of crud in the aftercooler tubes as well as the other corrosion issue I was describing. Good idea to service them anyway, as the air side cannot be cleaned any other way. Check out the site I mentioned prior to servicing, even if a "pro" is doing the work. Tony will explain why they should be well greased prior to reassembly.
Good luck, and Merry Christmas!
PS. I am no "expert" either, but I am repeating what I truly believe (after much research) to be good information.