Stupid Toyota dealer possibly messed up my differential

A mechanic at Tires Plus noticed a drop from the rear diff when I was doing the 50k oil change and an alignment. I have 50k miles on my Taco and the the last service on the diffs was at 30k mi. from a Toyota dealer.

I went back to a Toyo dealer (not the same one) to exercise the powertrain warranty. They told me the metal washer was missing and the diff oil was low level. They put a new metal washer on and topped of the diff at no cost. That means the rear diff was leaking (possibly for 20k miles). I read there's a lot of pressure and high temperature in the differential so wouldn't my differential be terribly worn?

It was the dealer's fault! Should I call Toyota, exercise the warranty and get a new diff?

 

Well, are there any issues with the rear? If not, I'm sure you're fine.

 

You say exercise the warranty like you are just going to say "Give me a new diff" and they will.
They will inspect it and tell you if if shows signs of wear or not...If you aren't hearing any funny noises or having issues with the operation of the drive train...I wouldn't worry about it. If there are issues down the road there is a documented instance in your Toyota records of where they messed up, so you should still be covered.