C5 Gearbox Slipping

That sounds rough! I had a similar issue with my C5. 'Wear fault' usually means something's degrading, like mechanical wear on the gears inside the transfer case. That can contaminate the gear oil and make it less effective. Is the garage saying anything about oil leakage or specifically about the gear oil itself? Maybe try an oil change?

They didn't mention any actual oil leakage, just the 'wear fault' and that the oil was the problem. So, you reckon it could be the gears themselves wearing down? Is that a big job? And would a simple oil change really fix it if the gears are damaged?

Yeah, that's what I reckon. It was defective gears in my case, that’s what caused the wear and the shifting issues. An oil change might help temporarily if the oil is just contaminated, but if the gears are actually worn, it's not a permanent fix. You'll probably need to get the transfer case looked at properly, maybe even rebuilt or replaced. Best to take it to a proper workshop.

Thanks for the advice. I took it to a specialist, and you were spot on – defective gears in the transfer case were the culprit. Cost me 330€ for the repair, but it's running smoothly now!