I asked my service guy at Five Star Ford and he pretty much told no superchargers or turbos, that as long as it doesn't mess with with the ECU, or can be directly traced to the cause of a warrantied issue, then it's ok.
Now, weather you can prove the diff was at fault or the driveshaft (for example) vs what the dealership is going to say... that's another story.
I've had a lot of friends that just keep all their factory parts in the garage for dealership reasons. lol
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