RC gearbox slipping

I had a similar experience with my RC. The transfer fluid seemed to be the culprit. It's like using the wrong type of oil in your engine; it just doesn't lubricate correctly. Have you considered an oil change?

Did your symptoms manifest identically – specifically, the slipping and unclean shifting? Was the oil change enough, or were there mechanical issues in the transfer case that needed more attention?

Yes, the symptoms were very similar. While the oil change helped temporarily, it turned out the gears were indeed defective, like a worn-out cog in a complex machine. I'd recommend having a workshop inspect it thoroughly to avoid further damage.

I will schedule an inspection at the workshop. The repair, including parts and labor, came to approximately 330€. Thanks for sharing your experience; it's been invaluable.