When soiling is of non-oil or grease nature it stays on the surface, common such soiling are dye stain transfer from blue jeans as an example; the first option with Prep-4.4 applies.
When soiling is obvious from body grease or spills, these are penetrated foreign contamination that need Degreaser-2.2 to emulsify or break-up the greasy or oily stains.
In both cases the areas are erase with Leather Eraser-4 to removed soiling particulates prior to Topcoat refinishing.
It is always better to start with Prep-4.4, if grease soiling is not obvious; then if after eraser-4 still finds shadow of the stains repeat with Degreaser-2.2.
The surfrace of the leather is to be absolutely clean prior to Topcoating, otherwise it seals and magnified the stain making it more obvious.
Does this explanation helps?
Roger Koh
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Roger koh