Just recently found this thread in a search as just few weeks ago bought new in box 8850 gg-1 .
I was surprised when it was turned over to take off the base to re-grease and oil it one truck had metal gears and open gear box the other truck has the plastic gear type on the 3 drive wheels the 2 idlers are metal the gear box open.
Been searching for a 2330-25 truck but seems like finding a needle in a haystack.
Either way it runs fine and the red n tacky has not leaked out the gear boxes so far.