I'm not sure if you have access to ancestry.com but there is the following name listed as having died in Georgia in 1957:
Name: Robert S Sederberg
Death Date: 11 Dec 1957
County of Death: Houston
Gender: M (Male)
Race: White
Age: 37 years
County of Residence: Houston
Certificate: 32841
There is nothign to link him to Illinois other than year of birth!
And his enlistment serial number would have been replaced by the O-... number upon his receiving his commishion as an officer. Similar to RAF practise, a new number for commishioned officers.
Drop a message to the AFHSO and ask what they might have about him.
http://www.airforcehistory.hq.af.mil/contact.htm
Regards and happy Christmas
Dennis