Mini Cabrio Gearbox Issues

That sounds suspiciously like what happened with my old SUV, a different brand altogether. It was exhibiting similar symptoms – gear slippage, rough shifting, especially noticeable when accelerating. In my case, it turned out to be the transfer case fluid. Have you checked the condition of the transfer fluid? Sometimes, mechanical wear can lead to the fluid degrading faster than expected. It's kind of like how the oil in a frying pan gets sludgy after you've cooked a bunch of stuff in it. How many kilometers are on your Mini?

Interesting analogy with the frying pan! No, I haven't checked the transfer fluid myself. Honestly, I'm not really sure how to, or even where to find it in my Mini cabrio. I'm assuming it's a sealed unit? What exactly do you mean by 'mechanical wear' though? Could it be something more serious than just needing an oil change?

By mechanical wear, I mean the internal components, the gears themselves, wearing down over time due to friction. Think of it like a door hinge that gets squeaky and stiff because the metal is rubbing together. If you're not comfortable checking the fluid yourself, that's perfectly understandable. I'd suggest taking your Mini cabrio to a trusted mechanic or a qualified workshop. They can diagnose the problem properly and tell you if it's just an oil issue, or something more sinister like defective gears in the transfer case. It certainly sounds like it could be that, based on your description.

Just wanted to let you know how it went. Took the Mini to a workshop as you suggested, and they confirmed it's the transfer case. Quoted me about 330€ for the repair. Not ideal, but at least it's sorted now. Thanks for your help!