I like the idea of a full synthetic as I think it burns cleaner. I was originally using the Yamalube when I first got this engine as I knew it was, at the very least, a "safe" choice. As I read more and more, I wasn't concerned about using the Yamaha brand. I started using the Pennzoil full synthetic as I had good access to it at a good price. But since Pennzoil no longer makes it (or at least I can't find it easily), I've been hearing lot's of good things about the Evinrude XD100 (full synthetic) - including what I read on a Yamaha forum (which includes some techs). I'll be switching to that - and it's not that expensive, either.