had air tank leak, pin hole

Thanks all, was never interested in repairing tanks.just cheap parts sources. I'm being quoted 1500, way scary price to drop a fuel tan and swap out an,air tank.

The walls of the air tanks are scary thin. It doesn't take much rust work to eat its way through one. Replace the tanks would be my suggestion, you can't Jerry-rig a fix on the one with a hole.

I would not attempt repair on an air tank that has rusted internally. You have no way of knowing how much good metal is left at any point.
Buy and install a new one, and make sure to drain the tanks daily when the unit is in regular use, and every time you build pressure if not in frequent use.

Pin hole is most likely from rust. I would consider replacing all air tanks and either installing an air dryer or serving the one on the rig that is not working.