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I guess i really shouldn't let it bother me, I guess the main thing is how well the grill cooks
Truer words have never been spoken.
All stainless will discolor when exposed to flames or heat above a thousand degrees or so. The inside of the grill is also going to get a nice layer of film from cooking smoke and moisture, you'll be able to keep this down but it'll never look like it did when you bought it. If you don't worry about it it'll get to a certain point, I.E. black and never get any worse. If you attempt to keep cleaning it it's just going to be bothersome for you in a vain attempt to keep it looking as new as possible.
It's a grill, you cook over open flame which produces smoke, drippings, moisture, etc, all of which do not lend themselves to that nice clean stainless look.
If I were you i'd forget about and just clean it up about once a year and be proud of making the inside look as bad as possible because it demonstrates your cooking prowness
And for the outside, a little dab of mineral oil wiped all over every two weeks or so will keep it looking better than new...