>> A << Piston Cup/Piston Installation

WARNING: This page is about a different car, the 2008 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.

Apply brake fluid to the entire inner surface of the release cylinder.
Specified brake fluid:

Brake fluid DOT 3 or DOT 4

Fig 1: Applying Brake Fluid To Entire Inner Surface
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
Apply grease to the piston and piston cups and insert the piston assembly into the release cylinder.
Specified grease:

Rubber grease

Fig 2: Applying Grease To Piston And Piston Cups
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.