Losing tranny fluid

2001 Lumina. 3.1ltr. lost all tranny fluid this morning. Was a gradual fluid loss. Was able to pull the codes on it. PO757 AND PO742. All lines are ok. Was able to see that the fluid loss is coming from a vent on top of the trans. It's pouring out while it's running. I know the codes reference solenoid valve. Just want to know if that's the problem. I can replace those myself. Talked to a trans. shop and they said it's a blown gasket inside. Gonna charge me $850. Any help on this is appreciated, thanks.

2001 Lumina. 3.1ltr. lost all tranny fluid this morning. Was a gradual fluid loss. Was able to pull the codes on it. PO757 AND PO742. All lines are ok. Was able to see that the fluid loss is coming from a vent on top of the trans. It's pouring out while it's running. I know the codes reference solenoid valve. Just want to know if that's the problem. I can replace those myself. Talked to a trans. shop and they said it's a blown gasket inside. Gonna charge me $850. Any help on this is appreciated, thanks.
You can always purchase a used transmission. Ask a couple of shops about the leak.