Watched my buddy blame his wife for their fridge stink for a year until he found his own rotten leftovers.

Wait, you used used motor oil on purpose?

My buddy Dave did something like this at his place in Tulsa, hung some kind of line across his sliding door after a robin kept whacking it every spring. Same deal, the birds learned to just sit on the line and chill. He figured it was fine until about a month later when one of them got spooked by a hawk and flew straight into the glass trying to get away. So the line stopped the slow flyers but not the panic flights. He ended up adding some thin vertical strips too so it looked more like a barrier from every angle, and that seemed to do the trick. Point is, the perch thing itself probably is not the problem, it is what happens when something scares them off that perch.