[alcyon]

Looking at the gears and the gearbox, this is my csi verdict.
You used too much grease internally. Also because the drive line wasnt sealed , all the sand stones and dust went in the gearbox. I wouldnt normally say this, but the gears look like they can run at least another 10 packs.
Why not use zippo and clean all the gears and gearbox, grease with hobby grease then reassamble.use a tissue paper and a small - screwdriver to clean in between the gear tooth.
Or if you can wait for new gears,then wait till you get them.