I use a Libmann brass-bristle grill brush on my Webers with porcelain-coated CI grates. I've read that Weber says that SS brushes are OK with PCI, but I don't want to potentially accelerate scratching. Always follow up with a wiping with a paper towel dipped in whatever oil (olive/ canola/ vegetable) is handy at the time. It might be my imagination, but I could swear that there is some transfer of the brass onto the grates during scrubbing. Wiping as a final clean seems to effectively clean off any possible transfer.