A very similar thing happened to me. Took my 2013 C-Max SEL to the dealership for an oil change, and they told me the axel seal/transmission is leaking (7 on a scale of 1-10). Seriously? My car is only 3 years old -- this should not be happening already. If anyone is wondering, yes, it is covered by Ford's powertrain warranty.
Finally got the appointment at a Ford Dealership, and they figured all they would need is a part... They gave me a rental car and told me it would be 1-2 days, tops. Called me the next day -- nope, need to pull the whole transmission out to get to it. What?? Um, okay. Call me a couple days later to let me know that since it is a hybrid transmission, that they deem it "untouchable" and ordered a brand new transmission... For FREE. Thank god for the warranty! Now, I wait. So far, it's been a week since all of this began.
The new transmission is quite a relief, because I was planning on taking the car in next weekend to get the transmission checked out anyway. Ever since I bought the car (bought it used in Oct '15, with 35k miles), let me just say -- it is the *loudest* car I have ever owned. Does anyone else have that issue? Highway seems okay, but slower speeds and idling, it just whines like crazy. I can't seem to find anyone else online talking about this. Any time I've ever had passengers in my car, that's the first thing they notice ("Wow, this thing is loud. You sure it's a hybrid?") The only thing I can compare it to is an adult-sized RC car! Hopefully, getting the new transmission will help with that, because it's incredibly embarrassing to be driving around a "hybrid" that makes more noise than most cars.