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40cpe is most likely correct. You can confirm this with a bit of quick work. Drain down the trans. Disconnect the shifting linkage. Remove the side cover. The broken tooth may have come out with the drained oil (use a screen to catch any debris for inspection) or it may still be sitting inside the gearbox.
You may or may not be able to see the broken tooth depending on the rotation of the gears. With the rear of the car up on jack stands, and the clutch fully depressed, you can rotate the gearset to watch every gear for damage.
If you discover what we already suspect, figure on removing the trans for a full rebuild.