The most likely cause is the heat. O ring chains are designed as low maintenance but to run in free air space to keep cool. The owner wanted to run the primary drive chain without oil but the general consensus is it overheated and let go.
He's going back to a plain chain in oil
I did wonder if the oil bath lead to problems with washing the lube out - but no oil at all means no leaks I guess? But even o-ring sealed chains need some lubrication.
