If you will look a the end of the stop there is a little slot. There is
a urethane rubber piece  that fits into that slot and acts as a bumper
right at the point where the door guide begins to turn 90 degrees for
the door to be pulled tightly closed. Without the stop, the metal in the
door and the turning mechanism can be damaged. It is one part that
should be replaced as soon as it fails. Installation is easy. It just
snaps into position.

Good luck,

John Rodgers
88 GL Driver

Jean-Woo Kim wrote:
> My 87 Westy's sliding door developed a popping noise each time I close
> the
> sliding door. It happens when it's almost closed and makes the inward
> turn
> to close shut. Prior to this development I noticed small bits of rubbery
> plastic pieces fall out of the area. Do I need the guidepiece (p/n
> 251843368)? And what's involved in putting this in? Thanks.
>
> Jean-Woo
> PS. I have access to carfax again.
>
>