I agree with "Farmquilter"........I have had the best results with Peanut Butter. It stays put and really softens the masking tape and won't damage the surface.

I use sewing machine oil to get rid of old dried up masking tape. I squirt some oil on and let it sit overnight.

Oil seems to be the consensus. Cooking oil is also good for cleaning nasty black grease like from working on a car off your hands enough so you can use soap and water after.
Rodney