I cam across a you tube channel (in french) of a car hobby mechanic who is attempting to repair a C6 with a blown head gasket. Although in frenc, the videos are more or less self explnatory and rather educational.
If I have understood correctly, he bought the car as-is, and if he can fix and sell it, any profit will go to charity.
The series is ongoing, all he has really achieved at this point (after 3 episodes) is changing the battery and breaking off 1 glow plug.
This one shows how to get into a C6 with a flat battery and seized lock.
C6 2.7 HDI head gasket job on You Tube
Moderator: RichardW