Create a table, put inside it all the ID's that appear on your map file ( not the vehicle models, the id="blabla" ), when they try to enter ANY vehicle, check if the ID is on the table with: getElementID, if it is, then check if they are in "Mafia" team with: getPlayerTeam + getTeamName, if they aren't, cancel the event with: cancelEvent.
You mean that you add the handler when you enter to trigger a function when leave, then when leave, you remove that handler, and when you re-enter, it says it's already added?
Post your script.