Just an update - going to pick her up tonight, I'm really happy that I have a good indy MB shop nearby.
It was the waterpump, so out it went along with the upper and lower hoses, t-stat, t-stat housing (metal) and I figured what the heck and had them replace the radiator with a new Behr with the metal reinforcements. So, it cost a decent amount, but all that stuff was weighing on my mind anyway - might as well do it now! Original radiator and original everything else actually too!
So, thanks again to all the people who helped me out. I like knowing a little about what I'm talking about with the mechanic. Thanks!