Rear Diff Noise after clutch pack change

[justinp16ex]

2016 EL Limited 4wd. Had rear diff clutch packs changed at a local dealership when I got the vehicle with 100k. I haven't had any issues other than just fluid changes in 75k miles. When I would change the fluid I would add two bottles of Motorcraft friction modifier. Rear end started making noise and vibration, fluid change didn't fix it. Now with 180k I took it to a local shop this time. They installed new clutch packs, after picking it up I took the vehicle on vacation. I was noise and vibration free for maybe 1k miles tops. The issue has returned,I told the shop, they said to get it in as soon as I get back, possibly a carrier bearing issue. Not sure why this wouldn't have been inspected when they had the diff opened. I asked how much friction modifier they used in it, I was told that they possibly only soaked the packs in friction modifier and didn't add bottles to the diff. I feel like this is the issue. My vacation was Wisconsin to Maine so I racked up those miles pretty quick. Sounds like they want to open the diff again and likely cost me more money. I'm tempted to just change the fluid when I get back and add 2 bottles of modifier. Any thoughts or advice would be appreciated. Hate to say it but I regret not going back to the dealership for this repair.

 

[justinp16ex]

Got back from vacation today, decided to test my theory before taking the vehicle back to the shop. I bought two 4 oz. bottles of friction modifier from the dealership, bought some gear oil at Walmart and changed the fluid. Saw lots of fine shavings on the fill and drain plugs. Nothing alarming, but seemed excessive for the 3500 miles since the repair. I drove a short distance to a place where I could do some figure eights. No more grinding and no more vibration. Now I'm wondering how much unnecessary wear occurred while driving 3500 miles on vacation. Going to talk to the shop tomorrow.