In 2003, on the way home from our first SE Alaska trip, I had a center window installed by the then C-Dory factory at Kent, Washington. It worked well for about 15 years, then no matter how tightened, it would drop down after a few bumps of the boat on the water. I thought like you, parts would have to be replaced, but first, thought I would try corrosionX, a penetrating lubricant. To my surprise, that solved the issue & I have had no problems since with the window dropping after putting it in the desired open position. That window & the original hardware have now been in the boat 24 seasons & functions just the same, as when new. I might add it’s been used a lot during those years & some here might even remember the incident of it being open, while we were exiting the tidal rapids of Fords Terror in 2004 & the video & write up of that incident.
Others might not have the same results, but perhaps worth trying, as it sure solved the issue for me.