Wait. What kind of gear “swells”? Is this a plastic “gear”? Frankly I have never seen a metal gear swell.
It’s not metal thsts for sure.....if they’d have spent that money up front this probably wouldn’t be happening.
Either plastic or sintered metal, which is basically powdered metal pressed into shape and heated to solidify. Still has a bit of a “spongy” structure. Perhaps the sintering was off and absorption of grease (I guess) causes a slight swelling.
That was my first thought as well. It is simply amazing where auto manufactures will use plastic these days.