Leaf scale was the first thing I googled and I only half agree. What doesn't fit is the damage. The damage being the white lines you see. It is always just the two lines/scrapes. It's like the scale is taking a suck and moving. My experience with scale is it multiplies but is stationary.
White oil, you say... sounds pretty innocuous. The plants are on my balcony. Because of wind and junk, dirt and dust and spray that gets kicked up usually gets in my face. I have little fear of innocuous white oil getting in my face.