Had that same problem with the rear axle seals on my previous 2002 W22. Seems like the axle manufacturer should have licked that problem by now!
Oil affects the brakes but probably not ABS, though the wheel speed sensor is there at the wheel and could also get oil soaked. Other than the wheel speed sensor at each wheel, all the rest of the ABS system is elsewhere.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL