NB Miata coolant leak question

Bringing this to the hive as my google skills are coming up short;

My DD NB has an intermittent coolant leak from the overflow tank. I've noticed a small leak/weep of coolant on the top of the expansion tank that shows up every few days. I've not noticed any correlation between it and the ambient temp or the distance i drive. My commute is about 25miles, and some days theres no leak, and others its there. Its never more than a small bit of green on the top of the tank and a small line where it ran down the side of the tank and onto the fender apron.

The factory temp gauge shows the temp as fine (i know the gauge sucks). My coolant level has not dropped appreciably in the 6 months I've owned the car. It sits just above the FULL line always. Its not showing any signs of overheating. I have not heard any gurgling that would indicate that the coolant is boiling.

The car has 62k miles on it. I have no record of any thermostat/radiator cap changes. The coolant appears to be the factory dark green Mazda coolant.

Is it possible that the overflow cap is just leaking and needs replaced? If it were boiling wouldn't it leak out of the small J shaped piece and not the cap?

I am unfamiliar with this generation. Is it an overflow tank or a pressure tank? An overfilled overflow tank can fill to the top during max heat soak ( about 15 min after engine turns off). The solution is to draw some out. If it is a pressure tank I would suspect a crack and I would do a pressure test.

I believe it's just overflow. The cap pushes on, so I'm pretty certain it's not pressurized.

Here is a pic of the cap and leak:

Pressure test the radiator cap

If it was mine, I would change the cap ( I don't have a tester yet) and lower the fluid to below the full line. If the fluid goes up again and the cap is good there are other problems.