First of all, you need to be comfortable with the possibility of things not working out. Getting contract options in OSUT is not a guarantee, and if you ship as an 11X with no options you are surrendering control over your destiny, and you may find yourself as a private on worldwide assignment. The 18X program does not just mean a shot at SFAS, the SF prep course is a huge advantage that only Xrays get, so if SF is your goal I highly recommend you don't settle. If circumstances force you into going to a unit and dropping a 4187 to attend SFAS on TDY orders, you are going to have to spend 12 months time on station before you could PCS to Fort Bragg for the Q course. There is already enough downtime in the course, there is no need to lengthen it.
However, with all those disclaimers out of the way, the SF liaison is right there on Sand Hill next to Winder Clinic, an area you will become familiar with, and they will give out contracts. Anyone with a 270+ APFT (or equivalent ACFT in your case), 110+ GT score, and no security clearance issues should be able to pick up a contract, but you have to do a two phase SF physical and it is thorough. We had guys come in with Ranger and SF contracts who were medically discharged (conditions existing prior to service) after that physical. You should confirm before you ship, ideally with the Sand Hill SF liaison, that you will be
eligible for a waiver with your specific condition.
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It can work out. Several of the guys selected in my SFAS class picked up their contracts at OSUT, including one of the best guys on my team during team week. However, none of them had sought the contract before they shipped and they had no eligibility concerns. The requirement for a waiver is all that makes this uncertain, so I would just call them up directly.