It seems like you are on the right track, the lighter the better. But rather than motor oil, I would think something as light as 3 in 1 oil would work. Very little resistance, and all you need is light lubrication, but not in a high heat environment like a car engine. I am working on a Space Mission which has an open gear box for the swinging target, and it has very little lubrication. But interested in what more experienced pinsiders think.