Ditto both of the above (Frank and Charlie).

Look closely at the cap insides for signs of tracking, like a pencil mark from the inside post on the 9 and 3 o'clock posts to the center. I see something, but it may just be the casting seam.

Most likely is the jet valve per Charlie's post above. A jet valve eliminator kit is cheap, and good insurance, and will not affect the engine normal running at all. I hate jet valves...

Not responsible for advice not taken...