Ironically the fatty spew is likely caused by previous treatment in an attempt to restore the holster. I have a mint Gerbirgsjager rucksack that HAD mint leather that is now falling apart due to liberal application of grease. In an attempt to preserve the item the previous owner effectively guaranteed its destruction.
"Numerous drawbacks are associated with dressing of skin products. For example, dressings frequently:
• darken lighter colored leathers
• encourage biological attack
• form fatty spews at the surface
• oxidize over time and stiffen the material
• wick into surrounding materials
• soften original finishes and decoration
• cause dust to accumulate
• impede future conservation treatment
• contaminate the material for future analysis"