In looking at the Mormon databases the children of Leonard began having their name spelled Gutherr. A Gutherr was originally used in the context of being the Lord of the manor and probably a nobleman. Leonard was not a noble although he did own the Manor Steinbreche and a small water castle.
The person you cite dying in 1821 was the a 4th generation descendant of Leonard and the name in the Mormon database is cited as Gutherr. Evidently, in the Bergisch-Gladbach records people knew the original spelling. In French one can find a reference to Gouthaire in relation to Lothaire (Lothar, a descendant of Charlemagne and King of Italy). Perhaps, the name derives from the name of the old king.
http://en.wikipedia.org/wiki/Lothair_Ihttp://books.google.com/books?id=-xwtAAAAMAAJ&dq=gouthaire&ots=kDjz3c7w-S&jtp=195