Grind going into third, drivetrain woes

[Halon]

I'd guess synchro. If the clutch wasn't fully disengaging, that could also cause it, but I would think if that was it then it wouldn't be ONLY in 3rd gear. You'd hear grinding in other gears as well I'd think.

Like Matt said, I'd replace the fluid and see if anything improves. But if I were a betting man, I'd put my money on synchro.