A very long drawn out link.
Do we have to guess,no I wouldn't touch a seal groove with a brass bristle brush either (especially on a small bore caliper)
If you live in a location where they put salt on the road you can do one of two things.
A. You can be ignorant wait until the corrosion has set in then try and fix it.
Of course corrosion often means the loss of material or the surface is compromised,sometimes to a point of end of serviceability (The seal groove and dust seal area are corroded beyond repair)
The same person would no doubt when pads had worn simply push the piston back into the body without cleaning the area where the seal contacts.
B. You check brake caliper condition,clean if necessary and change the fluid yearly,that would include any other items on a motorcycle that might be affected by salt or any other detrimental substance.
If the groove is only crusty a white scotchbrite soaked in white spirit would normally do it,if it takes more than that it might already be to late.
Fail that a simple length of small bore tube with a slit in it, air duster snout into the slit and up the tube 50mm or so,the other end into a box of baking soda,low pressure on a compressor if you have it and that will remove any deposit with no harm to the parent metal.