Problem with a Celestron C6 SCT

I have a problem with a relatively new Celestron C6 SCT (with XLT coatings). I bought it 6 months ago. When I used the C6 for the first time, it seemed to have a collimation issue. "Not big deal" I thought at that time. I put is aside and didn't use if for a while. Finally, a couple of weeks ago I decided to give it another try and collimate it. I read Celestron's instructions as well as several other from the Internet. This is not the first time I am collimating a telescope (I had a Newtonian reflector for a while). So I tried to collimate if the best I could and found that if the collimation appear good with the focus in, it looks bad with the focus out. And if I correct it with the focus out, then it gets bad with the focus in. When I look at bright objects, the difraction rings are always skewed to one side, and no matter how I try to adjust the collimation, they only seem to shift from one place to another, but never get smaller or centered. I have contacted Celestron to have the scope checked and repaired if necessary (this should still be covered by the two year warranty). But I am curious if anybody else have experimented a similar problem and what was the solution.
Regards.
S. Bucki

I found the culprit of my problem. It's not the scope (good news). The problem was the diagonal I was using. I noticed that whenever I was using this particular diagonal, I had to re-adjust the finderscope. Nothing seemed loose inside the scope, and the problem persisted with several eyepieces. I disassembled the diagonal and I found the mirror to be loose. I collimated the scope with another diagonal, as well as putting the eyepiece directly in the visual back (w/o diagonal) and now it seems to be fine.
S. Bucki