Miriam, now you've made me curious. I just checked my other shiny black machine, the Universal, that may not be a 15 clone because it's take up lever is on the front, not the side. It has a hole. I know the 301s and the Elna have, too. The Necchi has a hole with the lever on the front. Is that the machine that the Universal was cloned from? There are some strong similarities.
The tape is a dark gray so it doesn't show too much and it's working wonderfully, so problem solved.
Rodney, I'd be afraid of breaking the top of the slot off, so no pliers near the machine.
Snooze, on several of my machines, the thread jumps out of the bottom thread loop, but I don't argue with it as it doesn't affect the stitching.