I'm partial to Decker coal as I spend much of my time there
I've found that an old jigsaw blade works really well for cleaning out the air slots in the head. On several occassions, I've had the "T" that turns the ring quit turning the ring. It's because the "T" wears out the corners of the ring and can't get enough of a bite of the cog to turn. This could take several centuries. I've remedied that in snow storms by replacing the ring. I've friends who take the "T" out and build it up which also apparently works and doesn't lead to a bunch of old worn-out rings laying around. Note that mine is one piece, but yours looks like it can be easily detached to replace or build up.
I have had fines jam the auger up as well. I have to pull the motor/transmission to turn the auger by hand as the pin behind that silver clover shaped knob shears off to protect the transmission. I use welding rod for pins. I have a large ratchet fitted with an 8" long piece of square stock that fits perfectly and takes some of the pain out of turning the auger by hand. An auger with very sharp edges and wettish coal have caused these problems. Hopefully, none of these things will happen to you!
I turned my boiler off last weekend... just in time for some snow! Good thing I also have a wood stove. Thought maybe you'd hook your new Prill up during this cold spell. Hard to believe it was in the 100s elsewhere this week.