For anybody trying to understand the operation of the shuttle valve, page 11 has a sketch.

http://www.boatfix.com/merc/Servmanl/11/11a5r5x.pdf

It only has 1 TRV and does not show how the displaced shaft volume oil is vented, but the general idea is apparent. Following pages have the rebuild manual.

Other links.

http://www.parker.com/literature/Literature%20Files/euro_cylinder/v4/108_1301-uk.pdf

http://oemys-performance.com/media/autopark%20pump%20108a.pdf