58n63 From what I could understand modern gear oil may be too slick to let the synchronizer rings get enough friction on the gear taper to work like they should,may grind on the way in. If the shift collar dogs have weak worn springs so they don't put enough tension on the synchronizer ring may grind. You sometimes feel the collar go past the synchonizer then if you don't go back to neutral will grind. Always happens up town where people will know you don't know how to shift it !! LOL