I'm scratching my head on this one? it might be blow by? but it does not look like anything smoking from the exhausts, just the breathers?
I did try some straight 30 weight diesel oil, but I don't think that would cause the issue?

The owner is going to pull the spark plugs and send me photos, and then we will run compression and leak down test.
Other than the smoke, it seems to run well, and no odd noises.