I have an 06 E53, 122k miles

It has some bearing noise in the rear diff.

It's not super loud, but on a 1700 Mile road trip, competing with road noise, I particularly noticed it around 60mph and especially on Deceleration.

I bought the car with extended warranty so I took it to one of the warranty companies shops. They said the whole diff needs to be replaced. Warranty denied the claim because I do my own engine oil changes. Has nothing at all to do with differential failure, but it's their loophole to get out of paying claims on powertrain items now.

I talked to the mechanic and he said the bearings are "gone" and my cheapest bet is to throw a used differential in there.

However, I'm wondering, given that the mechanic never opened anything up for visual inspection, and that the noise isn't overbearingly loud, if changing the fluid would help the situation? Or at least add longevity to the car so I'm not in a rush to source a differential and install it?

Is it worth doing a fluid change at this point?

We have another 1700 miles to go next week to get back home...