Bem-- if you plan on doing it that often you might as well use Amoil tranny fluid and tap in a plug (like on your oil pan) so you can catch and reuse it. amsoil has a 100k mile life, just change the filters each time.

dont know why youd change your diffs that often the only reason the 1500s are supposed to change it every 15k is because of the F'ing C(U)NT clips, they have a habbit of falling off and then your teeth get all tore up...

 

despite the big G in the name
the G56 is a Mercedes built unit
not a Getrag
and finding those shavings is not a good sign

if it were mine I would check it frequently for the next
30,000 miles at about 10,000 mile intervals
and maybe invest in a Blackstone oil analysis right now
on the fresh ATF
to re-check against as the ATF ages.

it might also pay to investigate what lube fluid
Mercedes uses overseas in their G56 medium truck applications
...my gut tells me it may not be Chrysler ATF+4 over there

 

I have not changed the lube in my G56 yet. This summer I intend to change the oil in the transmission and both axles, bringing everything up to Amsoil standards. It's going to be expensive buying 6 quarts of synthetic ATF and 7 quarts of Severe Gear.

I wouldn't be too worried about shavings on the magnetic drain plug the first time you change the oil. I would say the magnet is doing its job.