Check out this CCI notes on caring and cleaning leather….
http://www.cci-icc.gc.ca/publications/notes/8-2-eng.aspx
http://www.cci-icc.gc.ca/publications/notes/8-4-eng.aspx
Both suggest that dusting with a brush, using rubber or an eraser is a good way to remove ingrained dirt. Using saddle soap or oils will cause leathers to harden and darken over time. Give a good read to these notes they have nice overviews of the negatives of using these soaps/oils on artefacts.
