The plastic door-glass frame-halves do not have a gasket and they were not sealed (at least not on my 2001 Hawk shell).
The glass is adhered to one half of the frame via silicone sealant and its pretty common for that sealant to fail on older campers like ours. It may leak for awhile but eventually the sealant will fail badly enough that the glass will slide down in the frame. Like this:
It's a relatively simple matter to remove the frame-and-glass assembly from the door and re-do the silicone sealant holding the glass in the frame. (I left the door itself on the camper for this but it's easier to re-install that assembly in the door with it lying on a table, particularly if you are working alone.)
The inner and outer frame halves come apart easily. You'll then see where a bead of sealant was used to adhere the glass to the frame-half. Remove the glass, clean out the old silicone sealant, and re-seal it. Then re-install the assembly in the door. (Note: You may also notice the plastic tabs at the bottom of the window are broken off. In my case, the window glass had broken loose from the frame and slid down, breaking the plastic tabs you see in that area. I put a small hard-rubber block under the glass to prevent it from sliding down again, should the seal fail again.)
An optional step (and one I took) is to also put a very small bead of sealant around both the inner and outer perimeter of the exterior glass-frame, i.e., where it touches the glass (inner) and where it touches the door skin (outer). I first put down two rows of masking tape to define that very small bead and pulled it up right away after running the bead and smoothing it a bit. (Note: The curves of the frame make the masking a bit of a challenge and I ended up having to use an Exacto knife to do some judicious trimming)
