This should be the last update on this thread, last night I finally assembled the car with all 6 subframe bolts.

Extracting the broken bolt was a steaming piles of a nightmare, it took roughly 8 - 12 hours of drilling, hammering and drilling again, a mate of mine and I were taking turns and he got the final blow to get the bolt out. Only broke one drill bit which was a surprise… but it finally gave up. I chased the threads on all 6 nuts in the frame to make sure. I put a tap through the mangled threads and a bolt fit in perfectly. For anyone wanting the front subframe bolt specs: M12x1.5mmx66mm galvanised steel. Apparently it’s tty but I have no actually written documentation to state that.

I used a normal hex head as a temp replacement, I’ve ordered 6 new subframe bolts just to be sure that this does not happen again.

Thanks to all for your input and knowledge, it’s very much appreciated.

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Current Garage:
BMW 2001 325i 5spd manual
BMW 2006 X5 4.4l N62