Sounds like the heat exchanger
housing cracked, someone repaired it with JB weld or an equivalent, perhaps gluing the bundle in place at the same time, inadvertantly or not, and now salt water
is mixing with fresh water
Unfortunately, I couldn't find even a parts
manual for the engine
, so it's going to be hard to help without a clearer idea of what's going on.
Replacement exchanger cores seem to be available, if the problem is with it, or they can often be repaired by radiator shops, if you can get it out...