Door not latching

Every once in awhile, at the most inconvenient times it seems, my driver's side front door will not latch when i close it. it is a 97 gp gt with 67k miles on it. it seems that whatever is supposed to be holding the latch in place is not latching, although after awhile it will latch again, this happens roughly once a week and i am not sure how to go about diagnosing or fixing the problem, any suggestions would be welcome thanks in advance.

try lubricating the latch, as over time the mechanism may have gotten gummed up with dust and dirt causing it to hang in the unlatch position. You may want to check the door striker post, and see if it has moved inward out of adjustment. This can happen if you've ever shut the seatbelt in the door.

i used wd-40 on the latch and checked the bar on the door, the latch point on the frame seems fine, it's in the same place the passenger's side door is in, it just feels like the locking mechanism that keeps the latch on the door from opening isn't catching. i am lost on this one.