Well, I had googled how to clean the white residue from zinc sunscreen off of car leather upholstery and the car doors from time to time, but nothing I tried worked. And I really don't want to spend $$$ on cleaning supplies. Finally found the tip to use a solution of laundry detergent to water 1:10, and scrub gently with washcloth.

Lo and behold: it works. I hope this helps someone else. I've been to auto forums and a lot of places, but only saw this tip in one place, and darn it I don't recall where I read it. But it works.