Can't say for sure, but it's probably not the synchro ring itself. There are three sliding bars that must stay keyed in slots in the synchro ring, and they are held there by two spring wires inside the synchro assembly. The wires wear down, allowing the bars to drop out of the slots.

If you take the top cover off, you can check for this. You should not be able to turn the synchro ring more than a few degrees with your fingers. If you can, something of that sort has happened.