Ive heard worth rubber care works very well. Go to autozone and look at all the products and get one that will clean plastic/rubber. A protectant will cover it until you wash it again, but something that cleans it and it wont come back.
have you tried mothers back to black? it works pretty good for me at removing wax i have drip on the plastic. a little tip i have dont be afraid to rub hard that way the towel or whatever you choose to use can get in the grooves and pull whats on the plastic up.