You could be losing it in a few different places. My guess would be at one or multiple spots at the connectors of the Rad Hoses. Ford has since updated these hoses but there are 3 of them and they're $75 each...so $225 for all 3. Also i had an issue with my last radiator(first one lasted 115,000 miles and i had the 2nd OEM Radiator went out in under a year.) The Ford OEM radiator sucks. Plain and simple. I have since installed a Mishimoto and I'm SUPER happy. Mishimoto has also come out with the 3 RAD hoses but they want $450 (Normally $550) but they are all C&C machined and have the double bell house end on both ends rather than just on one side as Ford has done. But what i found was happening to me was that my radiator only started leaking when it got to temps above 190. Which makes sense because thats when the thermometers activate.So it only leaked when i was driving. I had the same symptoms as you do now.