Worth replacing rear on 2K GT ???

I have 80K miles on my 2000 GT 'vert.

Some water got into the rear-end and the gears make a slight grinding
noise. I asked the dealer to change the diff fluid and check the gears,
but he refused to even look inside, telling me that he was sure I would
need a new $1,800 rear.

I really have no time to look around junkyards for a used rear and just
need a quick solution.

The car rides fine (for now). Should I just ride it out till the rear
goes completely or does it make sense to get the new rear now? Sell the
car as-is? (I've sort of been waiting for the GT500 to be available :-)
).

Thanks
Ron