Ancestry has U.S. Army Enlistments 1798 to 1914. With Ancestry you search Gosla* and you will get all the endings especially a "u" that can be transcribed as "n" or "w".
I find in Ancestry's index a in the Army enlistments a Gustus E.W. Goslan. The scanned image of page, the handwriting has Goslan but the first name is Justus. If you don't have access to Ancesrty or another site with this database I will transcribe it for you. They cite their source as: "Register of Enlistments in the U.S. Army, 1798-1914; (National Archives Microfilm Publication M233, 81 rolls); Records of the Adjutant General’s Office, 1780’s-1917, Record Group 94; National Archives, Washington, D.C."
Also he is listed in the 1930 census as Justus Goslar. In 1910 as Justus Gordan someone correct to Goslan. In 1900 as John E W Goslaw.