If I'm to understand correctly, what happens is that the seal between the water pump and the crank case fails, leaking water into the oil and vice versa. When the water mixes with the oil, it crates "sludge", which collects in various places. One of the first places to get gummed up is an oil passage that goes to the timing chain, leading to the timing chain being poorly lubricated. This causes it to break, which will typically destroy the valves and possibly the rest of the head as well.
Hence, use a really good filter and oil to help fight any existing sludge, and change the water pump to prevent any more from forming.
From what I've picked up, the easiest way to tell if there's a problem is that the heater won't blow hot air when the car is idling/not moving, and you'll possibly be able to hear the water pump making noise.
My Fiancee's Sebring has both symptoms...that thing is going to be an [expletive] to change out, I fear. :(