It looks like a smashing bit of rock art in this pic:
http://irishmegaliths.megalithomania.com/zSessKilgreen2.htm
but if this:
http://www.themodernantiquarian.com/post/33067
is the result of 20 years of being used as a cattle rubbing stone, it's a sad loss.
Have the carvings been as damaged as it seems from those pictures?
I sort of hope the apparent loss of detail is enhanced by the dryness of the stone, reducing the visibility of the carvings.