I think to remove deeper stains, scuffs, etc. may require something else. I haven't tried solvents such as paint thinner. What comes to mind is to first test a small spot using e.g thinner, turpentine , acetone or Xylene.
Xylene is a paint reducer used for various types of paints such as e.g. Chassis Saver, epoxy paints, etc. Paints such as Chassis Saver, epoxy paints, etc. once applied are impossible to remove using a paint thinner. Requires Xylene which is also used as a reducer.
I would also try some contact cleaner on a small stained rubber spot.
Chassis Saver S8 Reducer is basically Xylene which can be found at Home Depot, hardware stores, etc.
Some Fluke Dmms such as the 79 III the holster is part of the meter case, splits in half while opening the case to change a battery, etc. So I don't think there's anyway to replace a 79 III rubber yellow holster.
New Fluke rubber holsters H80-M normally run $50-$60.00+ however the H80-E doesn't come with a magnetic strap can be found for $25.00 (shipping included). I found one for my Fluke 87-V that didn't have a rubber holster.