The Nightingale Racher you refer to [1739-1803] was the son of Nightingale Redshaw [1711-1772] and Elizabeth Turner, his 1st wife. This Nightingale Redshaw in turn was the son of John Redshaw [1677-1752] and Mary Parker. His father and mother were John Redshear [abt. 1645 ? - 1721] and Mary [d. 1718]. John Redshear was buried in Layston, Hertfordhsire, but unfortunately no record has yet been discovered of where he was born.
And that seems to be as far as anyone has got.
The medieval village of Layston, whose site is near Buntingford, hardly exists as an entity, although the remains of an old church are still there - http://www.buntingford.com/layston-church/http://www.buntingford.com/layston-church/
I also assumed that the name was of German origin. But I have come to the conclusion that the German name Racher is purely coincidental [there are also Rachers in a few small hamletsin the Massif Central in France - but again I can find absolutely no connection]. If, however, one takes the various spellings and pronounces them with a local country accent, it seems much more likely that the original name was indeed something like Redshear or Redshaw and the Racher version simply became frozen with the more systematic orthography of the eighteenth century.
There appear to be many variations on the spelling of the name, even within the same branch of the family. John Redshear's progeny are variously recorded as Roger Redsher, Nightingale Redshower [another one], Mary Redsha, Nightingale Radshaw [and another], Joseph Redshear, John Redshaw and Nightingall Redshere [yet another] !!
The problem now is how to find where John Redshear/Redshaw came from. He was undoubtedly born some time around, or during the period of the Civil War when everything was in flux and transition and people were being uprooted from their traditional homes. There are certainly records of Redshaws in the Lincoln area and farther north in Yorkshire for instance. But it is hard to establish a connection. We need to find the missing link. One possibility may lie in militia records, but I don't really know where to start with this.
I hope this sheds a bit more light, but I would dearly like to know something more about John Redshear.