So I got have 04 600 with 8k miles on it not sure what oil the previous owner used. Now it has 13k miles and the past few oil changes I used non synthetic Castrol motorcycle oil. I now want to switch to full synthetic oil. Is it ok to switch over to a full synthetic given the year and that I previously used non synthetic? Also how other do you guys change your oil? I've been doing about 2,000 miles. Thanks!