To me that rocker cover looks so crusty that it now has rust pinholes which showed up the first time you drove it fast for a while. Because that is when the cover fills up with oil. My intepretation of the way the oil is sitting on the outside of the cover is that theres a pinhole at the top of each of the vertical streaks. Take both covers off to avoid getting rust in the engine, try tapping them with a hammer.. i bet it goes through... The aftermarket repro steel covers are OK. I would have just kept on topping up the oil and put in an online order for new rocker covers.
I would say deffo oil coming from rocker gasket ..when was it last off ...looks like the other side is leaking a bit too . Have you got any spare gaskets ?
It was really bad smoke. Covers were only off recently for an oil change. As above. Recently off for oil change. No spares. Am at garage now expressing my displeasure.