Hiya
I've got some photographs of those blue gloves doing things, but they're now worn out and were binned some time ago.
I've never been to the Pikestones, so my opinion was just from the picture. If this rock was under a mound - and we know it was a chambered tomb destroyed by a Victorian excavator - then that may explain, partially, the crisply incised line. The spiral motif - vitality - seems common in Bronze Age carvings.
The stone is Millstone Grit - it's also in our blood - and this scores highly on the Mohr scale of hardness. One of the stones in the Brown Stones row, nearby in Smithills, is carved with characteristic grooves. These, too, are relatively uneroded and fresh.
What about the egg-rolling rituals on Rivington Pike in the spring ?
etc.