Solution to "the mark of Schuberth"
My problems continued following my last post and so I sent an e-mail to customer service at Schuberth and they told me that one of the things that they are recommending is that you replace the liner in your C-3 with the same size S-2 liner.
They sent me an S-2 liner and it goes into the C-3 very easily and the swap was done in a matter of minutes. It simply snaps in place in the same places as the C-3. It fits very well and is much more comfortable than the original liner. They told me that there is a difference in the head shape between the C-3 and S-2 models and that for some people this is the only solution. It worked for me and they were very good about sending me a replacement S-2 liner at no charge. I have had this helmet for about a year and a half, I was most impressed with Schuberth's customer service. The helmet fits perfectly now and is quite comfortable. I hope this is helpful.