This simply oozes its great age.  The stone speaks to you covered in beautiful lichens.  So beautiful.  This never would have had an overthrow.  It has a small iron ring wherre the bucket lead would have been threaded.  Worn with the use over time.  There is an ancient diagonal crack in the wall in one place which I am loathe to do anything about as it is part of its life, its history but a pin could be quietly put into the stone if worried.  I think it is nothing to worry about but happy to do if required.  A simple overthrow could obviously also be added as required too.