Dirty sensor or damaged sensor?

Hi Folks.  I am a brand new Sony a900 owner. I bought the camera used and I am concerned that the sensor is damaged based on the consistent appearance of a discolored portion in one part of every shot with several lenses, exposures, etc.  I did the cleaning program on the menu several times, I used a blower as was suggested by the Sony tech folks and I still see the mark appearing.  I have posted examples in my gallery and circled the problem.  The person that sold it to me is willing to take it back for a 10% restocking fee.  If the problem is just dirt I have a repair shop clean it. If it is actual damage I think I need to cut my losses and buy another used camera with a proper sensor.  Please let me know and thanks in advance for any help.