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Yes, they do have some sort of oil or cleaner product on them. I have used them on the interior many times with no issue (on many different vehicles) over the years. But when I tried it once on the tonneau cover of the car, I discovered it was leaving oily streaks of some sort on the paint.
Since then I no longer use them on painted surfaces. However, they still work great on the gauge lens and in nooks and crannies around the center console. The wife's jeep has lots of small places on the center console and it proves a life saver there.
By the way - I also leave one on the keyboard of my laptop computer when not in use as well.....it does wonders keeping the keyboard and the display screen relatively clean. I have even gotten several co-workers hooked on leaving one in their laptops when closed/powered down.