Is there already a 690 Oil thread? I'll just open up the can of worms in here? Im using the same oil in my Diesel, Honda cars, RFS bikes & 950A. All with good experience. Long time between changes & higher fuel mileage It is Synthetic rated at 5W-40. How critical is the heavier weight for the 690? I see 10W-60 & 10W-50 listed. What keeps me from using the 5W-40?