Leap second is due to slowing of Earth's spin, not changes in it's orbit
I thought the reason why we had to add the extra second is because the Earth's rotation is slowing (i.e. the days are getting longer), rather than anything to do with the orbit of the Earth around the Sun. We add the extra second to avoid us gradually getting towards the situation where the Sun rises at midday.
Incidentally: "the Earth doesn’t always orbit perfectly". Is that so? It does wobble about a bit but I'm sure the Earth would claim that it always orbits exactly as it should.
