If you just want to clean off the years of oily gunk, I second the WD40. It will cut the grease and oil , but leave most everything else. Decals can be tricky if they are fragile, so be careful at first until you see what happens. I bought some nylon scrapers of Fleabay that look just like single edged razor blades, and they fit in razor blade scrapers. They work well to scrape off things like paint splatter or stickers without damaging the paint..
