And.... it worked!

The "small leak in evaporative system" was fixed by cleaning the gas cap gasket and firmly replacing the gas cap. No more light. It went out before I could even get around to clearing it, took a couple of days but remember I'm still waiting from my scan tool to arrive. (You can read codes via the odometer on my Jeep, but the only way to clear them without a scan tool is to pull the battery cable, and that causes everything else to lose its presets so I decided not to do that).