I think that the recommendation to remove them every year is due to the concern about finally getting them out. If we could document a final solution for removing them under any condition, the PM would not be required.

Due to the nature of an impact wrench and the brittle nature of the carbon deposits, I'm quite optimistic about this approach if one has sufficient patience to just hold their finger on the trigger for 1/2 hour. Also, don't just hammer in the counter-clockwise direction. If the plug develops some "slack", you'll accomplish the goal much faster if you reverse the wrench..........run it clockwise for a second..........and then return to counter-clockwise. The plug gets a "running start" and hammers into the packed carbon thereby further loosening it.

See how you make out with the impact wrench. Make sure you do not exceed 60 lb-ft. Err on the side of 55 lb.-ft.

Some have touted the use of PB to loosen the carbon. Might be worth a try.