Okay so my family raised me on homemade BBQ pits, and I've never owned a gasser, nor has anyone in my social circles... or family... blah blah blah. So I have NO IDEA how to help you, but it seems many others are coming up short as well, at least by the view count. I did find this: http://www.bbq-brethren.com/forum/sh...nesis+cleaning
That's what I got from searching "Weber Genesis Cleaning." Not a whole lot on the search from those keywords really, but hopefully this will help you.
I'll say this much, as far as grease goes... just burn it off. The rust, not really able to do much for you, as I've not experienced it on anything other than my COS, and I usually just sand it off and then I oil coat it until it starts looking bad again.