Very common for an intermittant ABS light to indicate a charging system problem. Too low voltage won't allow the ABS pump to operate properly, so the ABS faults when the charging system is beginning to fail.
Usually, ABS sensor problems are shown as ABS "functioning" at very slow speeds.
Try cleaning the ABS sensors, but unlikely...
I would have the charging system load tested first, as this is usually the problem that causes the symptom you have described.
1998 C230 "Black Betty"