After watching an occasional fuel drip slowly increase since I've been flying the plane, I decided it's time for a change. Step one was to fly a mission that burned my fuel down to a couple of gallons in each tank (thanks Skyview for the accuracy!). Next I removed the existing drain on each side catching the remaining fuel in a jerry can, replaced each drain with a new one, and replaced the fuel I captured back into the tank. No leaks or drips now. I suspect the seal on the old drains simply "rotted" away from disuse after holding no fuel for almost 4 years before their first fueling.
