My bolts still look good on the ST40 calipers. I regularly spray somewhat harsh cleaner (50% diluted grime reaper) on it pretty regularly.
Yeah, maybe you got bad bolts. Or they were dinged up during the install. I would remove the bolts and let them soak in some rust remover. Then maybe use some zinc spray on bolt heads.
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2018 F30 320iX Melbourne Red
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red
2000 E36/7 Z3 Steel Blue
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