A couple more incorrect guesses from the district manager of the local pool store (chain). He said there's some guy in his Texas warehouse that's pretty amazing at identifying stuff like this on sight, so he sent that guy my photos.

They said a replacement socket would be around $400 most likely (he didn't really look anything else, just guessed) and also somewhat of a bear to fish through under the concrete. Being that it's only 3 years old I'd hate to replace it anyway. That'll be a last resort if this miracle worker in Texas can't figure it out.