[HawgRyder]

I am not familiar with the Redline product.
The two things the gear oil needs to have....lubrication of course..and then some stickyness ( my brain fart for this morning) so that the syncro rings will have a little friction to work.
If the gear lube is too thin or maybe too effective in cutting down friction...then the syncros will not work as they should.
The fact that you see no damage to the ring...leads me to think more in the direction of the lube.
Did the previous owner use the same lube?
How long have you had the car?
If you made a change...then the last thing you did is probably the cause.
If the clutch is new...was the pilot bearing changed and lubed?
An old pilot bearing will keep the gears spinning even though the clutch is disengaged...and if it has enough drag...it will overcome the syncros.
Things to think about...good luck.
Bob