I broke that same plastic thing on my 180 a few years ago. I'm racking my brain trying to remember how I fixed it. Since I do not remember buying a new one, I believe I found both pieces, removed the set screw, glued it back together and then screwed it back into place. Surprisingly, it held just fine. I was just really careful whenever I shut my hatch from that point on to make sure it didn't get out of place and break again.
I do, however, remember the day it broke. Since the window won't stay in place without that part, I just removed it completely from the windshield for the tow back home. I was driving down the road and a guy next to me on the highway signaled for me to look backwards. Sure enough, without the window in place, the force of the wind opened up my sunsport hatch right up as I was going 70 mph. Totally freaked me out! Obviously, I pulled right over and surprisingly the thing never ripped right off. Certainly a disaster was averted thanks to that guy....
