When you change the brake pads you press the caliper piston back in, and it then works on the part of the cylinder that is subject to corrosion, the part that was behind the piston when the pads were worn. After replacing the pads is when it is most likely to seize.

If it isn't the piston in the caliper it could be the slides, ie the caliper not moving freely on the hanger. That problem is usually due to not cleaning it completely when changing the pads.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue