Yes Im thinking the issue is a result of the choke been stuck and the presence of the yellow gunk which im guessing is some condensed vapours from the oil.
Interestingly while ive been working on the Mule Ive also been trying to get my KLE500 motor bike back on the road which also has the carbies glued up with a similar residue. The bike has been sitting in a shed untouched for nearly 10years. Must be Kawasaki special oil.🤣
The yellow gunk needs to be addressed first, I'd say. If it's in the carb, it's probably gotten to the plugs as well.
I wonder if the ventilation tube isn't sucking up some oil on an incline.