So, let's say he's home quarterly? Check up on it when he's home - if it's at or over 3K, change it. If not, top off and change it at his next visit. I'd use Maxlife 5w20 or '30, depending on how much oil the 'Stang uses - it's cost effective but still good stuff, formulated with good detergents that will help fight the dirtier driving style the car will be doing.