@Jules V. Thanks so much for the info and especially the pictures! Like @bigssa I also have a C&B green performer. I checked the sweeps today and they look like the dirty SS sweeps Jules V. They are less dirty but the center H section looks exactly the same. So I'm pretty sure I have SS sweeps too!! Did they just include them on the C&B performers? I also have a non-C&B black performer deluxe from the same year (2010). That one is extremely dirty so I haven't check the sweeps yet to see if they are SS.
If your sweeps are bent upwards, remove it from the bowl and bend it downwards . Another option is to clean the bottom of the bowl and then place a heavy object on top of the bent sweeps to keep down. Leave it for a few hours or overnight.
No matter what sweeps you use, they'll eventually bend upwards if the bottom of the grill is not scraped regularly. Sweeps are no match for crud/gunk buildup especially from foods that contain a lot of sugar such as barbecue sauce.
See comments #3 & 6 regarding the years or models ss sweeps were used. The random ss sweeps that were used after 2009 were probably leftover stocks that weber used before they transitioned to aluminized.