86 Firebird gas leak at engine

Recently had engine work done at a local shop, on air vents. Now have a gas leak at the engine when the tank is full and car is level, or front is lower on a slope. After flow stops, gas will evaporate enough in a garage that in two months tank is empty. No noticeable leakage while driving or running on lwvel or with less than full tank. Is there a common problem or place I should look? Maybe a fitting is loose?

the tank vent is tied into a EVAP cannister in stock form. It sounds like either its been incorrectly bypassed, or there is some other issue, such as the vent line has ruptured ect

Not sure which air ducts you're refering to, so don't know how it would be related

Something is incredibly wrong. Gasoline left out in a 5 gallon bucket won't evaporate in two months. Basically your problem can't be happening unless its leaking so badly that there are massive puddles on the floor.

It sounds like you need a new evap purge valve. It should be closed in most situations (like when the car is off) which keeps gas from free flowing out of the tank ... and at this point, definitely a new charcoal canister. If its been exposed to that much liquid fuel its not very effective anymore.