Kerosene
Didn’t have any. I figured the sap on mine was from a pine tree and turpentine comes from the same place. I wiped it off this summer out in the sun. Came off easily. I wasn’t sure what the turpentine would do to the royal ex, so then I did an old fashioned yard wash with lots of suds. It’s shining like new in my classroom now.
Butter
My father’s solution for gently removing grease-like materials was butter or oleo. Dissolve the goo in butter and then wash the butter off with soap and water.
Turpentine vs kerosene
I’ve used both with similar results. I don’t have any preference other than the container that is closest or cheapest.
Alcohol has worked for me
I have use the ethyl alcohol fuel I use for my camp stove with great success. It has not damaged clothing and quickly removes sap.