MTFCA Forum

Will this cause any performance issues or is it of no concern?

That's pretty common and should cause no issues, assuming there is no significant leakage. It's probably due to worn threads in the cylinder head. Moving the plug to a different spot will acertain that. Some people wrap aluminum foil around the threads to shim the plug and prevent leakage. I've wrapped the threads in teflon thread tape to seal them and give some shimming effect. Chasing the threads would make the problem worse. I don't think modern day plugs have very accurate threads, so switching plugs around or switching to a different plug might help.

Odd that it is only the one hole.
P.S.-My arthritis doesn’t allow me to chase threads anymore!

Will rotate and check back in….

As to why one thread would be worn more than others, I'd guess that many heads ran many miles on worn out engines during the Depression and WWII and beyond. Worn engines, broken rings, worn out starters, if any, and old weak batteries, if any, may have required many owners to clean one or more problem spark plugs very often, maybe even every time they started the car and several times in between. A worn out plug in a worn out engine with bad coils and bad wiring and a weak magneto might have to be very clean to fire at all. Labor was dirt cheap, and parts were not. I imagine many a poor man carried his plug wrench everywhere he drove and wore his pocket knife or bent paper clip out scraping carbon-encrusted plugs. Items like anti-foulers and even trick spark plugs sold well, and some people would rig up an "intensifier", which was some devioce that held the plug wire about 1/16 or so away from the plug terminal to allow the coil voltage to rise higher and thus fire a worn or dirty plug. It worked, sometimes, sort of, at least until the coil secondary gave out.