When I click the play button, it just says "the video is not available"
Maybe the video is not available in my country (germany). I think you can change those settings when you upload a video.
I actually searched a lot for such a video before I disassembled the HD. But this one was never included in the search hits.
Anyhow, I dismounted the unit, removed the motherboard, cleaned everything, screwed everything back together. Aaaand: Issue is gone! Also the buttons are a little more firm now. The pad sometimes is not recognized, but I guess it is the general construction (which is kinda weak from my POV).
so, thanks everyone for your help.
cheers
chris