It could be sticking piston rings , pull the spark plugs, put 2 or 3 table spoons of Marvel Mystery oil or Seafoam into the spark plug holes and let sit overnight. This will lube the rings and cause smoke when you fire it up. But it may restore compression in that cylinder. Worth the gamble.

 

I give that a try, thanks.
you never know, ✅️

 

I’m crossing my fingers !