Model A transmission opinion needed

[Martinbuilt]

Hi.
Yesterday, i opened up my transmission to check and clean everything, before putting it in the car.
I'm new to these cars, and the one i'm working on is built from spares.
For the most part, everything looks pretty good. The only damage, and i think it's significant, is on the center gear in the cluster. I'll add a photo.
I didn't notice any wear, chips or pitting on any of the other gears. Kind of odd, right?
$425 for a new set is not in the budget.
I have 2 other gearboxes that i haven't checked. This one looked like the best candidate.
If i find a better set in one of those, do i use it? I don't know if mixing used gears is acceptable.
Thanks