No moisture and the coal is dry.
The burn is fine and there is ash on the end of the burn plate. No modifications of the holes.
my bad....i didn't mean if the holes were modified, just cleaned out. the manual recommends a drill bit to clean them and keep the air flowing freely through them. do you have about 1" of ash on the end of the grate or more?
If the burn is fine and you aren't getting moisture in the hopper indicating exhaust going through there, I'd check the door gaskets, then the gasket that seals the stoker assembly to the stove body. for the door gaskets, pinch a $ bill in it with it latched and see how easy or hard it is to pull it out while latched. It should not be easy.
if those are all sealed up, there isn't any other designed openings in the stove for the CO to get out.
Do you have access to a manual, if Harman has them on the website or I can email one to you. There is a decent exploded view of the stove.