text: Polyglot has a point : GR5A is shown along the Stekkerweg on www.groteroutepaden.be, but is missing to the east of the Tractaatweg on OSM. 
  Janfi also has a point, in that it isn't GR5, but GR5A.
  Upshot is that it would help if the route were walked & traced, then amended on OSM ; bit far to cycle from where I am, but there might well be a more local mapper who ... ?