Porsche 2012 911 GT3 CUP Technical Manual page 120

AP Racing provides a repair kit for the brake master cylinder
The repair kit includes the following parts:
4 -- Main seal
5 -- Piston shim
7 -- Secondary seal
10 -- Circlip
11 -- Rubber boot
Repair kit installation:
1. Remove rubber boot -11- and circlip -1
2. Carefully remove the internal components
3. Remove dirt / deposit in the cylinder
4. Coat the cylinder with brake fluid
5. Replace the following parts when rebuilding the master cylinder:
Main seal, piston shim, secondary seal, circlip, rubber boot. While
replacing parts make sure that all seals are coated with brake
fluid.
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