10W40 is perfectly fine as well.
If this makes you crazy then you should give up maintenance of cars.
Dude check out the previous pages. I have banged my head against the wall trying to explain the "science" in vain.
The coils were probably being eaten up due to bad plug towers in your M13.
M18 is a mouth watering prodpect for me too I wish we could get the J20 and the J23 here as well.
Your accelerator cable had excessive slack as seen in pictures.
Check your valve clearance. I'm 90% sure about it.