The earliest reference to this meme I have found is from 30 June 2004, http://groups.google.com/groups?selm=nuo6e01usbas8kiedqt2oo1ck38gmfh6hr%404ax.com.
It quotes from a web page. Here is an excerpt:
... Regardless of what actions ARPC contemplated when reviewing Bushs records, all options required that Bush be certified as physically fit to serve, or as unfit to serve. ARPC thus had to order Bush to get a physical examination, for which Bush did not show up. ARPC then designated Bush as AWOL and a "non-locatee" (i.e. a deserter) who had failed to satisfactorily participate in TXANG, and certified him for immediate induction through his local draft board....
Others have pointed out that most of the holes in the "Bush was AWOL" story were conveniently filled in by the CBS forgeries. Every person that studied the issue knew which holes needed to be filled.
In the fall of 1973, as an automatic disciplinary action, Bush was reassigned to the Obligated Reserve Section in Denver, because he disobeyed orders to show up for a mandatory flight physical and therefore was unable to fulfill the last two years of his six-year obligation as an Air National Guard jet fighter pilot.