in both my 2009 and 1990. I use Castrol GTX 10w40. Tried different viscosities but found 10W40 works best for me and my riding. The only thing I've found with using automotive oil is the clutch tends to grab when started in gear cold. After warm it's a non-issue. My clutch doesn't slip, never has unless I've been riding it in technical terrain. When I start my bike cold in gear, I just tap the start button to "break" the clutch loose. Haven't had any problems, both bikes have 32K on them now and I've had the 2009 since new and the 1990 since approx 18K miles. I'll stick to what works for me.