This was on Altercation today but I haven't seen it anywhere else. One of the reasons Bush has given for not taking his physical exam was that the F-102A fighter jets he was flying were being phased out.
In general this was true. Most units that were using them were phasing them out throughout the 1960s. However, Bush's unit used them until 1975, a year after Bush was to finish his guard duty. Therefore, the fact that it was being phased out doesn't seem like a valid excuse for him to not take his physical. They were still very much in use in his unit and were going to continue to be so until after his guard duty was up. Additionally, the other ANG unit that continued to use the F-102A until 1975 was Vermont, just a short drive from his new digs in Cambridge. It seems to me that he could have easily been assigned to the Vermont ANG to complete the final six months of his obligation rather than receive an honorable discharge considering the amount of money that was spent training him. Info on the F102A is here:
http://home.att.net/~jbaugher1/f102_2.html