So I think I've gotten an answer
I saw my Ortho #4 again- he's good- and he was looking at the symptoms a little more closely, went back and looked at the MRI, and saw that I split my post tib tendon BUT I split it very near the top- the MRI almost doesn't show it because it's at the very top of the field. This is why everyone was having so much trouble diagnosing it- the lower part of my tendon, that typically degenerates and leads to tendon transfer- looks great, & this is why so many doctors told me my tendon was fine. My ortho said because my tendon is split so close to the top of the tendon, and that the rest of the tendon is fine, I won't need a tendon transfer or osteotomy, just a repair of that area. So I AM looking at an unpleasant surgery experience, but he believes I'll likely be back to full athletic activity about a year after my surgery.
I'm considering this good news, in comparison to other potential outcomes I was worried about. I've already lost 1 year of running, but it looks like I'll only lose 2 (not 50
)! I'm having my surgery in Dec so I can heal over winter break (I'm a graduate student).