Driving with an axle leak is not particularly dangerous or hazardous to the vehicle, except in the case that the brakes are not performing properly due to fluid contamination. Vehicles with braking issues should not be driven. Concern should be taken for how long a component has been leaking. If the leak has continued long enough, the leaking component may be in danger of mechanical failure. If any mechanical noises are heard from the transmission or differentials, the vehicle should be inspected as soon as possible.
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