That's why you technically should replace any bolts that might be hard to remove later, or at least inspect them to see if the passivating coating has been rubbed off. If the hardware is abused (which is typical on oil pans) then the coating can be damaged and they will cause galvanic corrosion just like the manual says will happen with non-approved fasteners.
I replaced my trans pan hardware with bright zinc-coated stuff, which has worked fine so far. They're still bright.
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