FWIW, this worked for me
Like others, I was constantly plagued with the dreaded oil slick. I would open the case and clean the inside of the plastic screen protector with a micro-fiber cloth. But, alas, the slick just moved to a (slightly) different location. It was driving me nuts. I must have done this 20 times.
Then, I discovered that I must breath on the offending spot and then vigorously, very vigorously, rub the offending spot with the micro-fiber cloth for about 30-60 seconds. And that worked. Now, zero spots. Though I still fear that should I open the case, the spots will return when next closed.
I suspect (guess) there is a microscopic film residue remaining from the time the plastic was manufactured. It is not the cleaning per-se that resolves the issue, but the actual rubbing/wearing off of the film that did the trick.
HTH
Like others, I was constantly plagued with the dreaded oil slick. I would open the case and clean the inside of the plastic screen protector with a micro-fiber cloth. But, alas, the slick just moved to a (slightly) different location. It was driving me nuts. I must have done this 20 times.
Then, I discovered that I must breath on the offending spot and then vigorously, very vigorously, rub the offending spot with the micro-fiber cloth for about 30-60 seconds. And that worked. Now, zero spots. Though I still fear that should I open the case, the spots will return when next closed.
I suspect (guess) there is a microscopic film residue remaining from the time the plastic was manufactured. It is not the cleaning per-se that resolves the issue, but the actual rubbing/wearing off of the film that did the trick.
HTH