One thing not mentioned here is what you're using for towels. Most paper towels have enough abrasive in them to cause light scratches. I have been using Viva paper towels, they are softer and dont scratch the covering. Other than that I have been using automotive windshield washer solvent, even the cheep stuff is good enough to cut grease.

Wipe all the oil off the plane you can, use another towel to clean with the window washer solution and another towel to dry it. Do a section at a time, tailfeathers, fuse, wings etc. I may use 3-4 paper towels to clean a plane and its shiny clean when I get done.
I use Ultracote and have planes with several hundred flights on them that look like new.