Ford GT Gearbox Slippage

Slippage and unclean shifts do sound concerning, especially with that mileage. When was the last time the transfer case oil was changed? Has there been any noticeable grinding noise or unusual vibration accompanying the shifts? It could very well be gear wear in the transfer case but it would be beneficial to rule out simpler possibilities first.

The transfer case oil has not been changed as part of the routine maintenance schedule, which now seems like a potential oversight. Could the lack of regular oil changes significantly accelerate gear wear in the transfer case, particularly given the observed symptoms?

A lack of regular oil changes can certainly exacerbate gear wear. The oil lubricates and cools the gears; without proper maintenance, friction increases, leading to premature degradation. Given that the transfer case oil has not been changed as per the schedule, and considering the symptoms, defective gears in the transfer case do seem like a plausible explanation. I would recommend a visit to a qualified workshop to ascertain the fault beyond doubt.

Following your recommendation, I consulted with a certified technician, and the diagnosis confirmed defective gears within the transfer case. The repair cost 330€.