Thanks for the slicing tips. I think I need a skinnier poker. The one I have is a bit over 1/2 inch in width and does not fit in either openings that you mentioned. For some reason the grates only allow the openings to go so far, even when I had the stove empty with nothing on the grates.
One more question and I will be set. I tried pulling the knob to the thermostatic setting but it will not come off and I may have screwed something up with the sensitivity of the knob and numbers. I wanted to get the side panel off as you instructed to investigate leaks. Is this knob held on by a set screw somewhere? How do I check to make sure the setting of the draft door coincides with the number setting on the knob?
The correct poker is 5/8 wide and has an offset at the end. The slots are about 3/4 width so there is plenty of room for the poker. The shaker handle goes through a sliding plate which covers and uncovers the slots. To check why they do not open fully the stove would have to be cold. With a cold stove lift out the hopper and firebox and the two grates. Now you should be able to slide the slotted plate to see if it goes far enough. Maybe a small piece of coal has gotten lodged where it has to slide. If it is free and goes all the way then put in a grate to see what is stopping it. It sounds strange to me that all three openings are too small since the right hand shaker handle only controls the right opening while the left shaker controls the left and center openings. One side or the other should be working properly since they are independent. It is also possible that the sliding plates were put in upside down, though I doubt it. The shaker handle should go to the end of the slot provided for it. All the way to the left. You could also try swapping the grates though they should be the same. Another long shot is if the shaker handles were put in the wrong slots, but then the shaker would barely move. The uncovered slots are to the right of the shaker handle.
The thermostat shaft is a round shaft about 6mm with a flat on one side. There is no set screw. The round hole in the knob is cut away on one side and there is a steel clip that encircles the knob shaft and has a flat on one side to hold the knob on by friction. A bit of rust on that clip is holding your knob on tighter than normal. Push in on the panel and get your fingernails under the edges of the knob on each side and pull and pry with your knuckles evenly and it will come. Look for the steel clip as it may well come loose from the knob and you will have to push it back on the knob. Whatever you do, if you have to pry, do it evenly on both sides or you risk breaking the knob which has thin edges.
The thermostat setting does not have to be an exact thing because with practice you find the settings that work for you. My old stove was set so that the damper was about 1/4 inch open when the stove was cold and knob set at one.I usually ran this stove at a setting of 3. The newer stove has the damper set to just start to open when cold with the setting at 1 when cold. I run it between 4 and 5 depending on weather outside.