So I called my service guy and he looked it up.
Torque specs on 2015 , 250, Sterling non-limited slip 9.75 differential cover bolts.....33 ft pounds!
Pulled the cover, very slight wear on inside about 3/8 inch x by about an 1" long and a 1/8 inch deep groove from ring gear on cover.
Gear looks unscathed.
My guestion is what about the filings from the cover, they are fine and some in there, but do I need to rinse them out or something ?
Just wipe them off?
Anyway I got a tube of MotorCraft silicone, it says to let it put it together wet, where As RTV, has you go though stages of drying, then assembling.
Things looking good!