I agree with using the 6 point socket...12 pointers round off too much.

Last fall, my nephew asked me to help him put on a complete new exhaust
system with his Mi*ta, including exhaust manifold. This was a 12 year old
car and the manifold had never been removed.  He had tried sheer leverage
and heat and they just wouldnt come out.

I agreed but with the caveat that for a week, twice a day, he had to soak
the hardware with PB blaster and tap on them, each one, a minimum of 25
times.

When we got together to do the replacement, EVERY piece came off just as
easy as putting them on.

The complete exhaust system replacement took less than an hour.

Again, good karma and PB blaster.