If I previously washed out of an AFSC, would I be eligible to go back into that AFSC when my window opens?

Depends on the needs of the Air Force. If they have a critical manning need in that AFSC, they may re-accept you.

The short answer would be highly unlikely. It is a very rare occurrence, kind of like seeing Big Foot or the Lochness Monster. Once an Airman washes out unless the AF reaches critical manning shortfalls AND your current AFSC is wiling and able to let you go, then and only then with the approval of your current Commander can that re-application take place. But again, highly unlikely.

I agree depends on AF needs and if you are still in the AF or have been discharged. Several factors are at play. However, the best answer resides at the personnel office and your AFSC functional manager. Good luck.