Oh and there are other methods. Doesn't matter now though cause you have paid your money but.....
If you removed the sump, drilled the plug hole out to 14mm then filled it with a liquid metal ( found out today how bloody good Belzona is - go google em. Have an unlimited supply through work ) you could basically re-tap the standard size and away you go. Still Teflon tape and a fibre washer would have sufficed

Seriously you should take advantage of your grunts in the workshop - bloody engineers

Good advice from Mick though. Makes perfect sense but how many others would scream "Doh!!" before they realised they should have taken precautions? ---- Now there is a loaded question.