Hi and Welcome to Just Answer,
Ok, let's take a look at this;
I see that Joseph has OPTED OUT, I will see if this will help you further
What I think the problem is, is that the "Automatic On Switch" is failing as you suspect, here is the part you will need to replace
Also here is a parts layout to help you see what you need to do to get to that switch, see part 8-18 of the drawing. Once you have replaced the switch it should shut off normally.
More parts on your unit can be purchased here
If you need more help Let me know
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If there is anything else let me know, If not click accept. Thank You Michael L.