uhhhh first off what car is this for? and how bad is the shifting that it needs to shift smoother? If it is something like an 80's model vw, I've heard of people praising penzoil syncromesh. if its a honda, stick with 10w30 motor oil if I remember correctly. I have an 89 pathfinder with over 310,000 miles on it that is my daily driver. The 5 speed in it still shifts smoothly other than not liking to go fast into second when the fluid is cold. But I'm happy enough with it to leave it the heck alone considering its age.
