My wifes car only has 14k miles on it and the service light came on to change the rear differential fluid. We live in S Florida and I have heard that the fluid probably doesn't need to be changed. Any help would be appreciated. Also, the manual calls out for Honda ATF-Z1 fluid. Would the CASTROL IMPORT MULTIVEHICLE AUTOMATIC TRANSMISSION FLUID be ok? It says it is OK for vehicles that require the HONDA ATF-Z1 fluid. What do you think?

Very unusual unless the vehicle differential has made contact with high water or other possible contamination.

It would not be a big deal if you plan to change it yourself and the Honda ATF-Z1 should work fine.
Keep the receipt and log it in the maintenance section of the owners manual.

This car sounds like a communist plot to overthrow the government! I'd park it on the beach and wait for the tide to come in.