Actually, it IS a slinger...Think about a gear oil leak...that can run down the axle shaft and make it to the brakes. That piece of plastic is there to fling the oil off the axle before it contaminates the brake pads and/or disc. However unlikely that scenario may be, loss of brakes is an inverted delta (ie, failure can cause death) on the Failure modes and Effect analysis, so there MUST be a countermeasure.
