Knock, knock, knock sound

[1930 coupe]

I have seen people put 50 or 60 year old used fiber gears in a engine because the gear looked good. Most of these old used gears only lasted for 100 to 300 miles before the teeth broke off. My theory is that when the gear soaks in oil for 50 or 60 years it gets soft and the teeth break off when you try to run it.