I just saw an abstract of this article:Blaschke, Kristina, Lubricants on vegetable tanned leather: effects and chemical changes.
Restaurator: international journal for the preservation of library and archival material 33, 1, ( 2012 ) [eng w. eng; fre; ger summary] , pp. 76-99: 9 figs. (7 color), 7 tables, refs. It’s a study of commonly recommended leather dressing and their aging. Conclusion: they all age badly – don’t use them