New member here, just restored a 2002 18" Kettle. I'd seen your post, thinking that perhaps to get the shiny exterior back on my grill I'd try your mishap and apply cooking oil to the lid while hot. Well, during last night's (second) cook I managed to spill oil on the lid, resulting in a shiny spot very similar to yours. OK, so now it's got me irritated. I've been growing accustomed to the haziness and would prefer the entire lid to look that way.
This morning, I figured I'd give the degreaser recommendation a try. What harm could it do? It might work, it might do nothing or it might make things worse and I'd wind up applying cooking oil. Here's the stuff I have on hand, it's a generic version of Simply Green, available at Lowe's. I applied some to a cotton cloth and applied it multiple times to the entire lid (grill was cold). This stuff did the trick!
I wish I had before pics of the shiny blemish, but I don't.
In this after shot, you can barely make out where the shiny spot was, under my reflection. I still have a small area under the handle that I need to work on. It's difficult getting decent pics to show the area with the sun.
I actually kind of like the "dust covered" look of the patina.
Just figured I'd chime in here with my recent observations. As soon as I get a chance I'll post a thread on my restoration. There's a thread I've posted over in bbq brethren about it.
Regards,
-Dom