I am guessing that 90% of the rigs on the road that use gear oil, never get new gear oil. So 10 years in the bottle should be nothing. Yes, I would use it.
I wouldn't hesitate at all using that gear oil whether it was opened or not, as long as it was capped. Shake it before using. I have used much older without issues.
Oil in bottles don't go bad after a decade like people think unless it's some really awful group 1 formulation. But that amsoil is probably good for 40 years to be honest. Just shake it up once you drain about 2/3rds out.
This reminds me, I have a 40 year old unopened bottle of Valvoline 80W-90 gear oil. I have no use or desire to use it. I'll offer it free to my mechanic. His garage works on a large variety of cars and heavy duty diesel vehicles.