re
"Is the inner-working of the latch worn? "

Likely, and ........in order to possibly help you, to visualize what version
of the sliding door we're talking about ....
it would help if you say what year your van is. There are two styles of
sliding door, 80 to 84, and 85 and later. I'm guessing the later style. .

I would think it might be a matter of the mechanism being worn.  When the
part that pivots on the outside of the door turns,
a part inside the latch mechanism goes around a sharp corner on another
part 'catches' .  It could be worn there, or not moving far enough to catch
well.
or not lubed enough, and
    I find that it's necessary to remove the inner door panel to really lube
the forward latch mechanism.
The location of the part on the van's body is adjustable too I think.
Adjusting that could help too possibly.

----- Original Message -----
From: "David Klein" <david@ASHTEC.CA>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, September 18, 2009 9:29 PM
Subject: sliding door

> My sliding doors has been popping open "half" way when driving and
> driving on bumpy roads makes it happen quicker after closing. I
> lubricated as per bentley and it worked better for about half of our
> month long trip. I looked on the clearance on all side and it seems
> to sitting low in the opening but the strider plates are all lined
> up. The door had fallen off recently (previous owner) but was put
> back on by a good shop. I looked bentley about raising the door but
> it looks like the door is already raised as high it will go. Is the
> inner-working of the latch worn?
>
> Thanks, David