When I first looked into the bores, I totally bricked it as OMG, is that a crack in the walls?????!!!!!!!!
Luckily my son was not around as the amount of swearing that ensued was significant. Those observant amongst you may pick up on what I then realised, the mark is only where I had cleaned directly above is with some carb cleaner, luckily it was only a dirt mark
But it did totally throw me for a while. I will check the cylinders once parts come back from cleaning and if there are cracks or oval'ing then I will have the cylinders replaced