I picked up a NOS climax with gear problems. I'll buy new trucks, but it appears the gearbox is also slipping. I haven't popped it open yet, but the instructions for gear replacement only addresses repairing the trucks, not the gear box.
Are there some instructions for replacing other gears, not just repairing the trucks?
Side question, is this repair still available from the service department?
If it was bought "new" it's still under warranty. Send it in to Bachmann. They will fix it free.
Otherwise, here's a good start...
https://forum.mrhmag.com/post/how-to-repair-a-bachmann-climax-12212235