Does that window open?
If not, the simplest solution IS black silicone. If it opens and you want it to continue to do so, here is a trick. With the window open, tape plastic wrap over the edge of the glass window. Fill in the voids with black silicone (available at automotive stores) and close the window. That should squeeze the silicone and make a good seal. Remove the overflow with your finger and let the whole thing dry for a day or so ( with the plastic, the silicone will dry very slowly, you may need a few days depending on temp and humidity). When dry, remove the tape on the plastic and open the window.
You should be able to peel off the plastic wrap and have a decent new gasket.
When all is dry, you can trim the silicone with a razor blade if there still is overflow. or squeezeout.
Hope this works out for you.