Originally Posted by Clubscene

Spray it on the lock mechanisim on the door itself. Spray on grease might be a little better to use than wd40. If you want to do a really thorough job you could remove the door card and spray the lock moving parts on the inside of the door. Better safe than sorry, because if the door locks and cannot be opened it is a major headache that only a dealer or car lock enthusiast could sort.