Update:
I've talked to two of the support vendors listed on the DJI website. The first person I talked to, at Maxcopter, said that he didn't have the little black ribbon cable replacement part, because DJI had not yet released it as a replacement part. He was hoping that DJI would do that sometime in the near future, but he didn't have any specific information to base that on. The second person I talked to, at USHobby in Las Vegas, also told me that the black ribbon cable was not available from DJI as a replacement part, but he said that his company bought brand-new Phantoms and sold parts from them. He offered to sell me the ribbon cable for $200. In a moment of temporary insanity, I agreed. My "thinking" at the time, if you can call it that, was that $200 was a lot cheaper than $679 for replacing the entire gimbal/camera assembly. And I was hoping that replacing the cable by itself would do the trick. Upon further reflection, I decided that was a bad bet, because there was a good chance that replacing the ribbon cable alone wouldn't fix it, and I'm not handy enough or knowledgeable enough to know what else to do with it if the cable replacement didn't solve the problem.
So, I'm trying to cancel my order for the ribbon-cable and instead buy the entire gimbal/camera assembly. They want somewhere in the neighborhood of $790 for the assembly. (Don't quote me on the exact price. I stopped listening closely when I heard "seven-hundred and . . . ." The rest is a blur.) I told them there were places on the internet where I could get it a lot cheaper. They're going to call me back.
There are two vendors on the internet that I know of that offer the entire assembly: Amazon ($799) and Davesmotors.com ($679, but it's back-ordered.)
I suppose my other option is to just put the Phantom in the closet and wait for DJI to make the ribbon cable available as a part at a reasonable price. That way I could experiment to see if the cable was all that was needed and if that didn't do the trick, I wouldn't be out that much money. But I don't have any way to estimate when, if ever, DJI will make the ribbon-cable available as a part.
These first-world problems are tough, aren't they?