Possible draft issue?

I am willing to take any advice at this point. We have draft issues, I think. Hardin coal stove, located near Center ND, burning lignite. Been in the house 3 years so fairly new to coal burning. We are getting "smoke"/major sulfur smell when runing the furnace this year.

We have cleaned the chimney, horizontal pipe, and all ash related cleanouts that we know of. We did notice "smoke" coming from the doorish area this morning. There is a screw missing from the plate between the door and the furnace body, and a 1/4" gap in this area where the smoke is coming from. Could this be contributing to our draft issue? Are there other places that we need to clean out? Any advice would be greatly appreciated.

Pics are of door area where we can see a leak.

Yes you do have a draft issue. Chimney must not allow air in from any leaks such as a clean-out door or other cracks or gaps. Then some stoves will have a built in damper that would need to remain open until that sealed chimney was allowed to establish a good strong draft before gradually engaging/closing that damper.

What are the suggested places to check? We did reseal all the exposed horizontal pipe as we cleaned things out. We are hoping to get someone to come out and walk us through everything but options for coal furnace repairmen are limited.
I also would have no idea where to locate the damper.

The damper refered to above might be built in with furnace, look for a lever or some handle to pull out and allow gases to exit freely for establishing a good draft from cold start up. At same time allow some air to enter thru door spinner or gate to allow visiable flames to speed up warming the chimney to gradually increase the draft strength.
Your lignite coal needs air introduced both from above and below the grates

First things first.

Either look up the chimney with a mirror if needed during the day or place a flashlight shinning up and look down the chimney at night. You need to be sure that there is no blockage.

You have already checked the smoke pipe so next would be the furnace itself. Remove the smoke pipe and look in it you need to be sure there is not a internal blockage. (I burn Ohio,WV,KY bit in my stoker however I have had issues with "fly ash" building up in the heat exchanger and elbow pipe.)