This gray patch deserves a picture of its own. Namely you can see a little gray crater next to the larger hole at the very top. That is were our 12 mm zinc-coated carbon steel treaded rod was. When we tried to remove it with a pipe wrench, it broke off, not even promising to move. Well, then there was a second try. I welded a bar to the stump (it was above deck before) and then gave it a proper blue flame heating to possibly loosen any epoxy holding the bar stuck in its hole. There is a single M 12 nut (behind a metal plate) holding the bar in the transom. In the process I burned the paint, primer, epoxy fillet and fiberglass. And with a squeaking twist broke the thread again, clean off, but a bit deeper. What a pain. So we just drilled a new hole, slightly further up.