Grease on abs sensor

Well I am not sure what is going on here but I placed the replacement abs sensor in situ last week and it was recording the wheel speed but was slightly out of sync. The lynx said the air gap was too large. I got to it again and found it had a wee dollop of grease on it. I was under the impression that these things were meant to be squeaky clean. Would anyone know where this grease comes from? Does it come from the recording ring? Should I blast the area with degreaser or something to stop it recoccuring. Any help accepted.
Thanks all

wheel bearing

would the grease affect the reading?

no but they can take some fitting in fully enough if you remove them the locating tab can bend or i did have a too thick o ring on one once

jamesmartin said:

no but they can take some fitting in fully enough if you remove them the locating tab can bend or i did have a too thick o ring on one once

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Well when the abs sensor was recording a wheel speed I had placed the o ring above its actual position so I thought that repositioning the sensor back with the o ring in the correct position would sort it. Unfortunately, the sensor records no info now at all.
I am wondering if I should just take the o ring out altogether and seal it from above with a bit of silicon.
I am not sure why it would not record info after the refitting.