The early 55s and 111s also had that problem along with the pitted exhaust port. The threads were just cut too big and a few planes were lost when the plug blew out in a low altitude hover, the plug blew out of mine at about 5 gallons doing waterfalls. I guess there's a positive side to not having big enough cajones to tap the grass with your rudder or wing tips or rolling down the runway at 5 MPH, 5 feet off the deck, I easily made the dead stick landing while curiously watching my prop freely windmill coasting in. A Heli-Coil fixes the problem permanently and is pretty easy to install.

Plugs that I really would like to see are the ones where they are described as being melted off. I'm not trying to get people to send me their new plugs so I can put them in stock for sale, only used and suspect samples.

P.S. Joe, do not resist, you will be assimilated.