You could try using Meguiar's APC, I think diluted down to 4:1 may be strong enough to clean and not harm anything. I haven't used it in a while, so I can't remember. Something else you can try if the interior surface isn't too bad is Meguiar's Quik Wax; just spray onto a MF towel, then wipe the surface. I finally tried this and was satisfied with the results. It cleans, leaves some UV protection and it doesn't leave the surface shiny or greasy.