8. Attach a crescent to the flat part on the piston to prevent rotation, and
then unscrew the M6 x 12 mm cap screw from the bottom of the piston.
This releases the solenoid seal retainer and valve seal.
9. Discard the old valve seal.
10. Clean all oil and dirt off the components with a clean cloth and check that
the bleed hole is not blocked.
11. While the solenoid is apart, inspect the solenoid piston centre seal and
piston for wear, scratching or damage. Replace if required.