One cheap tip. Try motorcycle chain spray on the gearboxes, it sprays on, and then the solvent evaporates, this allows the grease to penetrate right down into all the bearings, plus it sticks like glue when it is dry. I just liberally sprayed my metal HL boxes, ran them, then soaked them some more. They certainly ran smoother afterwards and it was a lot cheaper than playing around with bearings and cogs.

My Tiger gets a lot of abuse on my own backyard tank assault course and the gearboxes are working just fine, the tank weighs a lot, it's fitted with metal gearboxes, metal tracks, metal hatches, and metal chassis strengtheners complete with metal suspension!

Hope this helps someone.

Cheers

Rob G