besides the synchro's, check for bearing play, check the fluid that you drained for any kind of particulate or material (check with a flashlight, put it through a paint strainer)
How long have you owned this transmission/how many miles have you put on it? It's a bit odd that the teeth on the hub for reverse are worn so badly, but the synchro for it looks like it hasn't taken any abuse...I'd think it would be the other way around, but maybe I'm wrong about that.
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