A couple of weeks ago my second hand EOS5D Mk1 suffered a detached mirror. Quick look on their website showed that this was a "rare but known problem" on this camera.

Rang up Canon UK to be told that it was a known and repairs would be carried out free of charge. I sent it off on Monday 23rd, had an acknowledgement of receipt by post on Wednesday 25th, and the camera itself came back yesterday, with new mirror assembly, new focusing screen, cleaned sensor etc. Excellent service!

(The value of the work was about £77 according to the parts/labour schedule - which I didn't think was excessive anyway, although that would have been subject to VAT and return carriage if it hadn't been done under warranty)