Is there any connection between your Sill research and the Pretzer name? An Anna Sill published death anniversary notices in the local German papers for an Albert Pretzer. Some other Sill names/references found in the German papers are Augusta Reichwald (née Sill), Hermann Sill, Louise Sill.
"Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950).
For more specific information contact:
Gary Rebholz, compiler/editor
Indexing Milwaukee's German newspapers continuously since 2007... helping to access our historic German-American culture.