I would bet it is a hose, expecially if one is rubbing on something somewhere. I had a 320 do that one time except I don't think it took more than 30 seconds to discharge. When a system blows or even leaks, it leaves oil behind,so if your engine compartment is reasonably clean look for evidence of a fresh oil leak. Freon is also a solvent so there may be a clean spot somewhere in a fan pattern. If it is that bad a leak, just charge it with air and listen or try the soap bubble method of leak detection, it actually works fairly well.