Hardly a rebuild as tbh hardly anything inside other than chambers and gaskets and plastic valves but vitally important to the running of the bike.
The reason for doing only because I took the lid off for plating and worried about seal as it was sort of cloth looking.
The new kit arrived today with instructions so split the two ends and removed the gaskets from top and bottom halves and cleaned the surfaces. Removed the 2 valves one in one out and then replaced them with new ones. Now they look awkward to do but they are not if you wet or lube the rubber grommet and there is a non through hole where you can put a blunt rod or backward drill bit say "mm diameter and just gently push through and job done. Replace gaskets with plastic one in the sandwich between and fit centre section and then same procedure with top one except it has a central split for the twin chambers. Refit top and 5 screws and torque back down to 3NM.
Don't use any sort of gasket seal on them either it says.
That is all my news except I also cleaned up the rubber pipe too . Big News that one.