So the title seems like an obvious duplicate or easy answer. But my question is actually a bit different.

I am trying to get a nut off the shaft of an engine. This is the "master" nut that secures the blower rotor to the engine shaft. It has a lot of (surface?) rust and it does not move. I have successfully managed to snap the almost 1 inch thick steel adapter for my impact in half trying to get it off. I used all sorts of penetrating oils, nothing helps.

I have been in a similar situation recently, I managed to unscrew it with a blow torch because I read in the manual that the nut in that machine was secured using thread lock and I assumed (knew) that heating it up to almost glowing hot would get rid of it.

This is where this question gets interesting. The nut is surrounded by non-removable plastic and that plastic is never further than 5mm away from the nut. So a blow torch is kind of out of the question. Here is a picture:

Everything black is plastic. I cant use a blow torch, it will melt off the plastic... What are my options here?