Yes I agree. Basically the dealer wants maximum reimbursement from the manufacturer so you don't have to pay as much so earn your business.
Just bare in mind if they have a long line of $100 oil changes in the queue, there isn't much incentive to tie up their techs to perform a repair that...
I also think window should be first, BUT i can see why the seatbelt is important. When the water rushed in, you'll likely panic and can't get seatbelt off, especially when you have precious cargo in the backseat.
That make sense.
So I'm guessing it's non serviceable item and once it's done, it's done.
https://auto.howstuffworks.com/differential5.htm
Were you really "playful" with all these snow?