Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › Man gear box oil change › Reply To: Man gear box oil change September 15, 2020 at 1:26 pm #963680 Richard KirshyParticipant Gotta love those life time fluids …. Providing your is not a sealed unit and depending on driving habits and conditions …. 30K – 50K should work out fine, just be sure to use the recommended fluid.