300SD: water in tranny fluid, but not radiator?

It is an 85 300 SD. The trans fluid looks like strawberry milk shake. I was toldin this NG that this is the result of a leak of the trans. oil cooler line within the radiator. So I replaced the radiator with a new one, ----not rebuilt, a new one. I have now replaced trans oil six or seven times. Each time about 2.5 quarts drains from the pan. It STILL looks about as bad. It doesn't take long to turn opaque/pinkish either, 10 minutes or so idle time while checking/ topping off the flud level, then 5 miles of driving will do it. How much water does it take to turn it almost opaque like strawberry milk shake? Because after all those flud changes and driving a few miles in between, I have not seen the slightest drop in the coolant reservior level (I drew a line on it). If water is getting into the tranny fluiid, it is bound to cause an apparent leak in the coolant level, right? I can't think of anywhere else water could get into the trans flud than the radiator, right? Is there nothing else that could be causing the tranny fluid to look like this? Is it time to spend $75 or so to have the tranny flushed (which I'm thinking probably will be a waste of money)? Is it possible for the fludi to look like this if it is full of microscopic bubbble? If I let the contaminated/removed fluid sit in a clear jug for a few days, would the water separate out to the bottom? Maybe there is some simple test? The tranny shifts OK. It has always upshifted to second kind of hard, and the only difference is that I am noticing a pretty hard downshift back to first now....seemed that it used to be smoother. I have a new filter and gasket for it, but I am waiiting for the last fluid change--- fluid having cleared---before changing the flilter. thanks, Jim