Gentlemen,
The M6 in my '98 Z28 doesn't shift as smooth as I think it should. With 83K on it I know the synchronizers may have some wear but I was wondering if anyone knows of any additive made that might help smooth it up?

 

You could try some synthetic ATF if you can actually get ahold of it, it's usually pretty hard to find. I think redline makes some but it's pretty expensive. I'm not sure how much it will help but it's worth a shot, since I've noticed that shifting is a lot easier in warmer weather, so a synthetic that is a little more consistent may help. I don't think there really are any additives that will help. It's probable that some company has thought up something that says it makes it easier to shift, but you can't replace a synchro assembly with fluid.

Also, you may want to make sure that your clutch hydraulics and other components are working properly, a lot of the time they can slowly fail over time and make it feel like you're having trans problems when it's actually the clutch only partially disengaging.