Thanks for all the great suggestions so far. They are extremely helpful. My responses to the issues laid out:
1) Yes, it has been way too long since I changed the coolant and that is likely contributing to the dirty color and needs to be changed regardless.
2) Numerous signs are pointing to the heat exchanger. There is a bit of a sheen on the water from my wet exhaust (even after warm up) and I noticed that after running the engine for a while, there wasnt any pressure on the radiotor cap when I was doing the test this time.
There are two heat exchangers on my engine...one smaller one for the oil and one larger one I assume cools the engine water coolant. I imagine it is a good idea to get both tested. One would think that the leak would be at the oil cooler, but the confusing thing to me is that it is cooled by raw water and shouldnt mix with the engine coolant. Possibly both are bad as the oil cooler sits in front of the raw water coolant....maybe oil comes in to the system from the oil coolant leak then gets into the coolant from another leak in the fresh water/engine coolant cooler downstream?