About 2 years ago I was dealing with a warranty issue on the 3500 series that required a fitting to the heat exchanger to be replaced in some sort of recall situation. Sorry that I can not remember exactly what it was. Pantropic Palm Beach handled it for us as I was doing a million other things at the time. I would call your local CAT dealer to ask if you really needed to know.
Apparently there was a law suit issued against Cat by some charter fishermen Yachts that had serious heat exchanger failures, never did find out the resolution but have seen it mentioned a few times..on different sites
From a BoatUS Magazine article, May 2007: "... a class action lawsuit filed in January against marine engine giant Caterpillar on behalf of owners of 1996 and newer C-12 and 3196 engines. Included are an unspecified number of other Caterpillar turbocharged marine diesel engine models. Over the years, these units have been equipped with eight different aftercooler designs all of which, the plaintiffs say, crack, leak water and cause corrosion of internal engine parts...."