If you can wash it, use the hottest water you can.Soak the strap in it the rinse well.Then soak it in Vinegar and don’t rinse—air dry and it should work well.Good question…..
This will remove any inorganic oily stain:
1.) Circle the stain with dish soap.
2.) Spray the stain inside the circle with WD40.
3.) Allow to set for 20 minutes to reactivate the oil.
4.) Using an old tooth brush, scrub the stain with the dish soap circle. You MAY want to add additional dish soap at this time.
5.) Launder as usual.
I KNOW this works, I’ve done it.
GOOD LUCK!!