Hi Johan;
Just noticed this thread. I run 6/1's exclusively on WVO (except for starting and stopping) for 12 hours/day (I am running 24/7 right now, i alternate engines between day and night) I find that I need to de-coke every 2,000 hours or so and need to clean the injector every 300 hours (at oil changes). My oil is dewatered, heated and filtered before going into the storage tanks, then it is pumped over into the day tanks - every time I take the oil off the top of the tank, never the bottom.
I have over 15,000 hours on one 6/1, around 10,000 on the other The second is now due for a decoke (not responding well to loads) and the most I have done is to replace rings at 7500 hours in #1 engine.