Welcome Aboard!
The case is magnesium. I doubt that there is any "rust through" warranty on it. Since the warranty for the vehicle is likely expired, you might not have any luck with a request for warranty service, but it never hurts to ask in case there is a quiet recall or extended TSB oon the problem.
My 2000 runs in salt spray 6 month out of the year, and has no evident corrosion. I just had the case out last week to repair the transmission.