I have the same problem.....rear wiper hanging down....wont stay in position. havent tried tightening it yet. Ill give it a try and use some lock tight also. Ill report back my results since this thread is very thin.
I just fixed it, Easy fix, theres a plastic cover over the nut, it rotates up to allow access(pry up on the end, curved piece), I used some loktite Threadlocker Blue 242 on the treads and tightened it back down. I do have a new small issue, when I tested it, it rubs on the rear wing, we have winter type blades on it and i think they are to thick. Other than that its working fine.