You can probably reuse everything when you replace the pads. They should have a hole in the top to press in the sensor, follow the other end, plug new sensors in there too, very simple.
The anti squeak grease is applied to the back of the pad, where the caliper piston comes in contact with it, also on the metal sides front and back, just don't get any on the pad itself.
I forget the minimum rotor thickness for the 126's and my cd-roms no longer work.

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83 SD

84 CD