Some little turd egged our motor home a couple weeks ago. And washing that thing is a major project. After washing it off I noticed it got down in the driver window. I took Goo Gone and squirted it in there, left it for about 2 hours and then the egg just rinsed right off. Goo Gone is made with the oils from orange peels, all natural and it didn't hurt the rubber. I've used it on the boat for grease and it works great. Worth a try and you can get it at Kragen, WalMart, K-Mart, Target, just about anywhere.
Lisa