Over the past few weeks, the sliding door on my 1987 Westie does not want to close properly.  More specifically, the latch at the rear of the door does not want to lock onto the post mounted on the body.

If I slam it hard and push inward at the rear of the door at the same time, I can usually get it to latch, but it is becoming increasingly difficult.  A couple of times the door has popped open while in transit, which is a bit unnerving.

What is the solution to this?  Moving the post?

Rick