Snapped off GP, I think. W210

[muleears]

I have read all the broken glow plug threads I can find but I don't remember seeing this situation. I was removing #5 after easily replacing #4. 5 was taking a lot more pressure to loosen. I had used plenty of PB Blaster and I was working on a hot engine. Finally enough pressure was applied and I heard a snap and it appeared to come loose. I began backing it out, there was still significant resistance but the ratchet could be turned with one hand. I kept going and going but the plug was not backing out. Still resistance like it is, but it is not coming out. At that point I stopped and decided before I screw anything else up I would come here for advice on my next move. Is it snapped off and is this the normal failure mode?

I know from the other threads there are methods to drill/tap/etc and get the broken off plug out. But this is still one whole plug. Apparently it is separated above the threads as it won't back out. Where do I go from here?

PS: Pulling the head is not an option.