In date 15/03/2012 I decided to do a collimation process for my C8, following the instruction of Thierry Legault in his fantastic webpage: http://legault.perso.sfr.fr/collim.html
This was the situation before
As you can see the diffraction pattern is definitely asymmetric. Working on the three screws on the secondary mirror, I succeeded in obtaining this:
Really better, but not perfect, so I finished the job with some more little adjustments.