http://www.partsamerica.com/ProductD...rtNumber=11623
This is for the 67-70 non-locking cap. For a 72 it might be vented, and then the parts store should be able to cross the non-locking to a locking and vented if needed. If the cap is not vented, drill a tiny hole in the cap, but the system may be vented (if it has a charcoal canister in the front under the batt or on the other side a non-vented cap is what you need). I hope that isn't too confusing, but GM did three different things here, non-vented cap, vented cap and vented fuel system. Figure out what you have and use the link above or hit up your local NAPA, Car Quest etc.