Earlier today I performed an oil change on the GTR. As I unbolted the sump plug I didn't notice a problem, cleaned it up and put it to one side. Did the rest of it like oil filter etc. Last thing to put back on the car was the sump plug. Screwed it in with my fingers with the brand new Copper washer slotted onto the plug. The copper washer touches the side of the sump and the plug just keeps turning in my fingers not getting any tighter. Began to unscrew the sump plug again and it slid straight out of the drain hole. The threads on the bolt are find but inside them were the threads from the drain hole. Has this happened to anyone else? The only two things I can think to do is get someone to weld up the existing hole with the sump off the car and tap a new hole or buy a new/second hand sump. Any recommendations? P.S. I'm told can only go the welding option if it's alloy, anyone know if it is or not?