After my mysterious coolant loss and reading about several others with a similar situation, I decided to replace my coolant reservoir over the weekend along with the new, updated cap. It worked, no more coolant loss.
While I was in there, I went ahead and replaced all of the spring clamps with real, screw on type clamps (a TSB says to replace them if they leak, but why wait for a leak?). When I pulled out my tank, I could not believe the number of stress cracks in the thing.