Help with the differential

[Villafane]

hey guys, i accidentally drained the fluid for the front diff. of a 2004 ML350. i drove it for about 50 miles, and it started making a horrible grinding noise, and that it just suddenly stopped, and it continued to do this even after shifting into neutral and trying to tow it with another car. what i want to kno is, a) what could the problem be, and b) how to solve it

thanks a ton
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