question about my weird gas cap

So my old 1983 Camry came with a gas cap that has a hole in the middle with a trap door mechanism where you can insert the gas nozzle without unscrewing the cap. BUT recently the trap door has become rusted and wont close. Is this bad for gas pressure? Ive never heard the hissing sound when removing the cap, so does this mean it isnt holding pressure? Time
to get a new gas cap?

I would get an original equipment replacement cap. I don't think that cap is original equipment.