DS3 Gearbox Slipping

Whoa, that sounds worrying! Slipping gears are never a good sign. When you say 'transfer case oil wear fault', what makes you think it's specifically the transfer case and not just the regular transmission? Have you checked the transfer case oil level and condition? Is it dark, sludgy, or low? If it is, an oil change might help. However, if it's already slipping, defective gears in the transfer case may already be the culprit.

Thanks for the quick reply! How would I check the condition of the transfer case oil? Is it something I can do myself, or do I need special tools? Also, what are the chances that an oil change will fix it, versus it being a more serious mechanical issue?

Okay, so checking the oil condition usually involves locating the fill plug on the transfer case (it's often a bolt or plug on the side) and removing it. You might need a specific wrench or socket. Then, you can stick your finger in or use a dipstick to get a sample. If the oil looks or smells burnt, it's definitely degraded. Honestly, with those symptoms and the mileage, and without being able to properly diagnose it myself, I'd say there's a strong possibility it's more than just the oil. Defective gears in the transfer case seem very possible. I'd recommend taking it to a trusted mechanic for a proper inspection before you make anything worse!

Thanks for the advice! I took it to a workshop, and you were right. It was defective gears in the transfer case, and they quoted me 330€ for the repair. Appreciate the help!