KDXme
Like you said, the book states that you should use either 10W30 or 40. Some of the guys that post here have mentioned using Automatic Transmission Fluid because it makes a smoother shift. I didn't have much luck with straight ATF, but a mix of 50% ATF and 50% 10W30 seemed to work well for me. I have no experience with synthetics though, sorry. Good Luck, I'm sure someone with more experience can better help though, maybe check the archives for this subject, I think its come up before.