Vehicle had ABS fail caution lights and uncommanded braking on 2007 Mercedes-Benz R350

This is secod time this vehicle has had ABS cautions, only on the occasion there were also severe uncommaded braking actions accompannying the light when it came on. My maintenance guy has told me that the problem is with the front axle tone rings being cracked and giving false signals to the ABS sensors. We have been trying to find a ay to purchase the tone rings separately, but now it seems we may have to replace both front axles. Any help or insight would be appreciated. anyone know where we can purchase the tone rings separately? Thanks

Asked by for the 2007 Mercedes-Benz R350
not avail to my is what it is.good luck