Without knowing the price per litre paid (and converting to gallons), there is no way of working out the MPG. Just to illustrate that; if the OP paid £1/litre, he used 690 litres (151.78 gallons) therefore MPG would be 24.95. If he paid a more realistic £1.15/litre, he used 600 litres (131.98...

I had the same issue about four years ago and successfully helicoiled using a 22.5mm drill to clear the hole, then a M22x1.5 tap. I can't see what size the actual helicoil is as the label on my packet has deteriorated but there are tables online that will give you that information. But these...

I put mine at the base of the ‘B’ pillar, which you can see when you open the front doors. It’s away from any engine heat influence, and subject to outside temps as it’s outside of the rubber door seals, but not in direct air flow, so protected from wind blast, direct sunlight, or any damaging...