Gearbox oil & differential oil viscosities are very different, so quite large particles will be dragged out with the oil, not so with an engine where its preferable to have warm oil to aid extraction by whatever process is being used. There's also usually a magnet to collect the expected swarf in a differential, as well as the unexpected swarf!
 
A new member has recently posted about shards coming out the drain plug of his gearbox.
Never hurts to have an occasional 'deep delve'.
I have seen many parts on magnetic geabox drain bungs, normally a fur tree of swarf, but on the odd occasion a bearing or bits of brass/bronze, all trucks still running to my knowledge.
LT77 always seem to have a fur tree on the drain bungs, assume the r380 is the same?

Engines slightly different.
 

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