Got lube?

I just had my 4 speed rebuilt and he said to use any 90wt gear old, but NOT synthetic because then it will be too slippery for the synchros and you'll have a hard time shifting.

The way he explained it that the synchros are like a brake, they're supposed to slow down to match speed so you can shift. When they're too slippery and can't slow down, then it's hard to shift.

That's what he told me at least. I'm no expert at this so maybe someone else can verify if it's true.