How hard is it to get it into reverse after its all heated up?

I would think if the issue was excessive drag on the input shaft, then it would grind A LOT when going for reverse.
If reverse seems pretty normal, and you could get another gear(like 3rd or 4th) normally, then I would think there is an interface problem with the brass ring and cone for 1st gear.

What happens when you try to go from reverse to first?