Thanks very much Daniel for figuring all this out. I've been running our C-Max back and forth to the dealer for months and am hoping that today's visit will be the one where they finally figure it out. So far they're insisting they can't figure out the problem because their scanners tell them it's running the correct software but I haven't been able to get them to verify it's actually the correct modem that was installed during the recall a year ago. If it's still not working when I pick it up this afternoon you can bet I'll be digging out that TCU to verify the part number myself later tonight.
Update: Dealer got the part this morning so I took the car over and they replaced the TCU/Internal Modem. It's back on MyFordMobile now and working perfectly.
So - important notes for anyone troubleshooting this. The part # on your TCU probably starts with GM5T. It seems this old part # sticker is still used on the new TCUs and in Ford's parts ordering system it is still starts with GM5T and the "engineering part number" (some sort of internal number) also starts with GM5T but the new part number starts with GM5Z in some of the recall paperwork. Super confusing for the service writers and techs - Ford is really not doing the dealerships any favors in the way they are handling this recall.
There is another part number sticker on the TCU, I didn't get the whole part # but the important two characters are AD or AG. If you see AD - you have the OLD hardware and it will not work. Even though the TCU takes the new programming and the onboard diagnostics say all is good - IT IS NOT GOOD. The diagnostics are lying. You need the "AG" part number.
I will try to get my TCU back out and take pictures of these part number stickers but in the meantime if anyone is having trouble getting their dealership to be able to fix your MFM problem tell them to make sure the correct TCU is installed - just because they did the recall doesn't mean they used the right hardware.
If you just can't get them to understand, tell them to look for notes from a technician named Tucker at Rowe Ford in Westbrook, Maine. He and I figured this out and he should be able to explain this all to the service department at any dealership who is struggling with this fiasco.
Good luck to all, I'll keep monitoring this thread for questions.