On the all or nothing question, work out the equation that involves condition of your seals, personal preference and money.  My bias is if one seal was dry enough to split, others are probably not far behind.  On the related question, the roll-ups can all be done without disassembly, but not the wing windows.  Easy project.
GoWesty link:
http://www.gowesty.com/product/door-window-seals/23441/seal-kit-for-front-roll-up-windows-?v=
Click Videos link for walk-thru of the install procedure.
Click Related Articles to a link Window Moldings on Vanagons for overview.

From: Mark Belanger
Sent: Saturday, September 1, 2018 10:58 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Upper Front Door Window Seal Showing Age

Greetings V'all,

On a recent camping trip, I noticed the seal around the upper right
passenger window was splitting, as shown here:

 <https://postimg.cc/image/45voltqi3/>

I know I need to replace that part, but is there any conventional wisdom
about the need to replace the entire seal kit or just limiting it to the
part in question?

On a related question, I know the upper part can be replaced by just
rolling down the window, but does the full kit require more disassembly or
just rolling down the window?

Thanks much,
MB
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________________________________________________________________________
Mark Belanger - mbelanger@gmail.com