Not sure then take digital picture first to see what goes where.
Replace the syphon the menbrane it's split and I've never messed with changing just the membrane espcially if it's the old type.
If you are game for the following:
Low level
1.Turn off water feed to cistern
2. Bail out the water from cistern
3. Remove the flush lift bar by un hooking from the handle lift arm
4. Undo the large flush tube nut then the syphon retaining nut. Pull the syphon from the cistern.
Fit new syphon note the position/s of sealing washer/s
Close coupled
1.2.3 above
4. Remove the water feed pipe from side/bottom of cistern.
5. If cistern screwed to wall [2 screws rear top inside]
remove the cistern to pan securing nuts
6. Lift the cistern clear of the pan. Note the large doughnut shaped seal this will have to be renewed.
7. Lay cistern on it's back side and undo the large nut holding the syphon in place remove the syphon.
Reverse instructions for replacing new syphon. Get one for either cistern that can be repaired in situ.
Nobby
January 2009