When applying Leather Degreaser to the Leather, the oils are dissolved. A fine white powder appears on the surface. The oils absorb into the powder for easy removal. When a grease or oil stain has built up gradually over several years, it cannot be removed in a few minutes. Your patience is necessary to complete the job.  Several applications may be necessary. Also, stains left untreated for a long time may have caused additional challenges like loss of color. Degreaser may also be used on textiles. Always test for colorfastness.