Except For STI Model

NOTE: Before installation, remove the pad clip and remove mud, foreign matter and rust from the caliper body assembly and the support - rear disc brake.

Apply a thin coat of grease to the support - rear disc brake.
Grease:

An item contained in the pad kit, Molykote M7439 or equivalent

Courtesy of SUBARU OF AMERICA, INC.
Check the brake pad. <Ref. to INSPECTION , Rear Brake Pad.>
Apply a thin coat of grease to the pad clip, both sides of the shim - disc brake rear inner and the shim mounting surface of the pad - disc brake rear.
Grease:

Pad clip (A): An item contained in the pad kit or equivalent

Shim and pad (B): An item contained in the pad kit or Molykote AS880N

Fig 1: Identifying Grease Applying Area On Pad Clip, Shim And Pad
Courtesy of SUBARU OF AMERICA, INC.
Install the pad clip.
Press back the piston with a disc brake piston tool as needed.
CAUTION: When pressing back the piston, the clearance between pad and disc rotor becomes large, which makes the brake pedal effort softer.
After the installation of rear wheel, be sure to perform the adjustment of the clearance and the pedal effort by depressing the brake pedal several times.
Install the pad - disc brake rear.
NOTE: Install the pad indicator in proper direction.
Install the caliper body assembly.
Tightening torque:

27 N.m (2.8 kgf-m, 19.9 ft-lb)
Install the brake hose bracket.
Tightening torque:

33 N.m (3.4 kgf-m, 24.3 ft-lb)
Install the rear wheels.
Tightening torque:

120 N.m (12.2 kgf-m, 88.5 ft-lb)