doesn't matter when you shut it down, at that point the fuel will stop flowing anywhere (injectors closed on injection system, no air through carburettor) so cannot cause problems.

'borewash' will be caused by massively too much fuel entering the cylinders (much more than be burnt by the amount of oxygen that is in the cylinder). or from a leak in the fuel system somewhere that contaminates the oil. that's basically what borewash is, it's a degreasing effect from too much fuel in the oil