When I was inspecting my car before purchase, we found a streak of dried coolant on the side of the radiator plastic end tank. These don't fail as often as the ET but are known to fail between 120K and 150K miles.
Edit: 3 years and 40,000 miles after radiator replacement, I was chasing another leak, only to find it was from not tightening the ET cap enough! (And maybe also from ET not sealing properly to base plate, still not sure on that one.)