How to remove snapped off plenum clean-out cover screw in Quadrafire Classic Bay

[sksmass]

I was cleaning my Quadrafire Classic Bay and managed to twist the head off of the screw holding one of the exhaust plenum clean-out covers (part 410-7910). The plate came off fine but the screw is still in the hole so now I can't affix the cover.
Three questions for the more experienced out there:
1) is there a trick to remove the remains of a bound screw? I have tried heating it with a torch and lubricating it with light oil. And vice grips. Should I just give up and drill it out and replace it with a larger self-tapping hex head screw?
2) if I can manage to get the screw out cleanly, what is the proper thread and pitch machine screw to replace it with? 8-32 or 10-32?
3) is there any way I can run the stove in the meantime by, for example, using ceramic magnets to affix the cover, or maybe jerry-rigging some heavy piece of metal to lean against and support the plenum cover from inside the firebox?

 

[johneh]

If you can not get a hold of the broken screw, drill it out and tap it to whatever size you need. The new screw: you want a stainless steel screw

 

[silverfox103]

I'd be a little "gun shy" to use a stainless steel screw, especially since you just broke a screw. You'd have a real issue if you had to drill out the stainless screw.

Tom