Passenger side of door does not always lock in my 2002 S model

[MSEagan]

I love my 2002 S model. It was one of those special $9,999 deals (5 speed manual). But, there is this problem with the passenger door. When it is locked and then shut, it often does not actually lock. I have to go around and lock it with the key. I have taken it into the dealer and it always works fine when they try it which is frustrating. This was a problem from the beginning. Has anyone else had this?