my suggestion - which seems a tedious workaround - is to have separate actions for each vehicle, all pointing to the same script copy/pasted. which, thinking about it, wouldn't stop the actions popping up in the player's menu.
an even more lengthy workaround would be to have a script running in the background when the player enters the pen, tracking said player's progress and continuously monitoring his/her distance from the given vehicles. when s/he is close enough to one, add the action, further away, remove the action.
it does seem very pissy doesn't it. the third alternative is to go with THobson's suggestion, and alter your logic accordingly to fit with the game limitations - i.e. repair is called from inside the vehicle, but also triggers a 'get out' animation.... also makes some limited sense, as you're going to know when the vehicle needs repairing only on getting into it.
unless it has wheels missing, or is on fire...