Oncidium Nanboh Waltz black streaks

[fragrantphals]

I divided a friend's oncidium Nanboh Waltz (Makalii x Ornithorhynchum) and kept the old growth and gave her the piece with lots of new growth. The old growth has black streaks on both sides of the leaves, as if someone took a black pen and made lines on the leaves. The new growth has beautiful unmarked foliage, even the mature new growth on newer pseudobulbs. I think the plant was from a big box store. I hope it isn't a virus, but I don't think it is because the plant was grown in low light conditions for at least 1 year and the lines never showed up on the new growth, even under that stress. Has anyone seen this on Oncidiums before, and what is it? It is apart from my other plants now but I would like to put it under my lights with the rest of them. Thanks!