Al,
I would start with an inspection to see if the fabric is legal. From there I'd get into the logbooks and find out what exactly the finish is on the wings, that will tell you what you should and shouldn't use, including the manufacturer's recommendation (if they are still around.) Failing that, car wash soap and a sponge and water should clean much of the dirt. As to what to repaint it with, that goes back to what is on the wings now and what you are hoping to achieve. I believe Stewart Systems is approved to top coat any existing finish.
Good luck!
Jim