You are on the right track. Check out "Life History of Henning Rathjen" by Norma C. Starritt (c1980, Shepparton, Victoria Australia, page 12-13) where there is an English translation of Linie C Family Estate in Eck; "Die Familien Ratjen/Rathjen aus dem Aukrug, Kirchspiel Innien" (Reimer, 1936, Schleswig-Holstein, page 58). This translation records Johann Rathjen b1771, married Wiebke Ratjen in 1798; Johann died 1845. Johnann and Weibke had a daughter Wiebke born 1812, who married Hinrich Kock (Koch) of Kellinghusen. Wiebke's younger brother, Henning, was born 1826, and died 1912 in Australia; he married Caroline Brunke in 1857 at "Sandhurst" now known as Colbinabbin near Bendigo, Victoria, Australia. Henning and Caroline had nine children, their descendants are now alive and well in several country towns across Victoria.