I believe this post by Charmalu is good info ..
"""well in the FSM Volume 2 under windows sec 67 it details how to properly
install front and rear windows. for the front window, it is installed dry, and then under#19 "Between glass and sealing frame, and between body and
sealing frame, seal with MB window sealing compound".
for the rear window as per #16 "Make seal between glass and rubber frame as well as body and rubber frame with MB window sealing compound
part# 001 989 31 20".
I took out my rear window last summer because of a leak in the trunk. the
gasket had been in their 9 yrs, time to replace not going to mess with it.
bought a new gasket, had window cleaned ready to install. called a mobile guy to install. charged $150.00, put it in dry. said MB doesn`t use sealant
so when the winter rains arrived I needed a bilge pump in the trunk.
I bought some 3M window black urithane sealant. fits in a cailking gun, ran
a bead under the rubber from the center of the roof down to where the corner of the trunk meet. then between the glass and rubber. dry the
rest of winter. I think the tube was $14.00.
charlie """
from
http://www.peachparts.com/shopforum/diesel-discussion/195480-re-seal-windshield;-do-yourself.html