Sunroof pops open
 

I have a 1986 560 SEC with a sunroof problem, and couldn't find an answer in the archives.

When driving down a bumpy road, the sunroof will drop down at the back. At highway speeds on a smooth road, it will get "sucked" up and open. Closing it again in either situation is no problem, but it happens repeatedly. The sunroof works perfectly otherwise.

Someone told that this was due to worn plastic "bridge" pieces. Where does one find these pieces, and how difficult are they to change?