Just did the first oil change on both my recently purchased 2007 Outlaw 500 ATV's. The price for 2 oil change kits was $90! The owners manual dictates an oil change every 10 hours using Polaris PS-4 or equivalent. Does 10 hours for synthetic oil sound reasonable? What is so special about this oil? Any suggestions for an alternative? I can't find any info on the quart as to the weight of this oil. Can't do $400 a month in oil changes, but would like to keep possible warranty hassles at bay. Any suggestions would be appreciated.