2001 Chevy Monte Carlo Oil Filler Cap Stuck/Broken?

I tried to remove my oil filler cap off of my 2001 Monte Carlo (3.4L engine) today in preperation to change my oil, and the cap wouldn't come off. The engine was cold. The cap seemed to only want to turn ~90% of the way. After a little bit of forcing, anger and then leverage with a large wrench, the cap still will not turn further.

I am not sure about the construction of the oil cap, but my fear is that an internal part is broken, and the threads are not actually moving at all, but only the top of the cap. Even applying pressure down on the cap and then turning is not helping.

I have resolved my self to taking whatever measures that are necessary to remove the cap (Breaking the top of and then removing the screwed in piece) and purchase a new one, but the last thing I want to do is break something off and have something drop into the oil pan, as this would be relatively tragic and require a lot more work on my part.

Any suggestions would be most welcome.

Thanks.

Pat Murphy