Help with phantom radiator/coolant leak.

I'm confused -- you said "it always drips from the cap/overflow bottle area when I park, but I can't find a leak" -- isn't the 'leak' the dripping from the overflow bottle? What am I missing?

If you're not having any other symptoms (lots of 'steam' from the exhaust that smells like antifreeze), leaks (heater core's not leaking into the passenger compartment is it?), coolant's not getting into the crankcase (oil looks like a chocolate milkshake), it's not overheating -- you're probably just overfilling it. My resevoir tank has "MIN" and "MAX" lines on it in both my cars. If I fill it past the max line, when it heats up, pressurizes and expands in the system, it will overflow the resevoir. Try continuing to drive it around at the 3/4 level you mentioned and see if it stabilizes there with no other symptoms/overheating. If so, take a permanent marker and mark the tank with it hot and cold so you know where your "fill" line is.

Every now and then it's an easy answer/fix.