After five and a half years of heavy use, my main computer, a mid-2011 27″ iMac, is on the Fritz.
It is currently unclear if it is the graphics card itself, some related hardware, or just a worn cable. Maybe I am gonna be surprised and it is something completely different. What annoys me most is that it could be related to an call-back from 2014. I did not notice the re-call at the time and it apparently expired in 2014 (that is the reason why it is only available in the WayBack Machine).
I already emailed a local authorised service provider. Once I hear back from them, I will bring it in to get an analysis and a quote. Based on that, I will see what my options are.