Couldn’t it be that if the resin feels ok when you stir it it would be ok for printing? Which resin is it?
I would definitely pour it in a new tank though.
But it would be really really helpful if you would post detailed photos of the condition of the tank after it’s empty of the resin, since it’s surely past 3x it’s standard lifetime. A lot of us here would like to know more about the failure modes of a tank that has been exposed to resin for such a long time.