I'm replacing the locking gas cap we had on our '94 Acclaim. I checked with Stant's site for part numbers and they specified two different ones for the car, one "regular" and one "Pre-Vent" cap. Site gave no clues as to what the difference was, neither did their application book at Wal-Mart. Called their tech support line from the store and they wanted to call me back. I just bought the "regular" cap figuring I didn't want a venting cap on my fuel system. Any clues as to what a "Pre-Vent" cap is?