Is anyone using a synthetic oil in their 650? And if so which ones? Does it make a difference as long as it is 10W40. I noticed that Castrol Syntec is $4 and change a quart while the Suzuki dealer is getting $7 and change for theres. Can anyone shed light here? The book calls for an oil change at 3000 but not a filter. Anyone doing this. I have always changed filter with oil. Dealer wants $10 for filter anything cheaper? Lots of questions but I know you guys know lots of stuff.