Consolidating deteriorated leather

Does anyone know of a treatment for old leather-bound books whose
covers are deteriorating? I am working with our Rare Book collection
at my library, consisting of volumes, many of which are from the
17th-19th centuries, that are fully intact but have covers that are
dirty because their leather has dried up. I need to be able to
reduce the residue that comes off the books and have them be clean
to the touch. Thank you in advance for any suggestions

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                  Conservation DistList Instance 11:15
                  Distributed: Friday, August 8, 1997
                       Message Id: cdl-11-15-011
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