The front sensor sticks into the Birfield housing. It's going to get covered in grease in there. It should most likely be grease with moly in it, from the packed Birfield (CV joint), and it's usually black.
If the only thing you've done is install a lift, I don't know how you could have...
Oh, well, the ABS on these doesn't have much of a record of failing, so there's no club to join. Probably the most common (still uncommon) mode of failure is for someone to damage one of the front ABS sensors when trying to remove a Birfield, or having one taken out by an exploded Birfield...