Bloody heck! Broke off in the hole!
I don't fancy this new fangled oil pressure switch if they break that easy. At least since it hadn't been tightened down hard the stub would have come out easily. Reminds me of the old 12V Zener diodes that were made of copper and had a torque spec of 4lbft. They would break off if you sneezed when you were tightening them.
I didn't realise that post '98 they have a different connector. I haven't had the one off the ST4s yet but it's definitely made of plated steel. In the event of it needing replaced I'll be off to the motor factor for a suitable match.