You have got what I wanted to do to my old Mk4 the central console, hand steering a 50 is a sod!
On the valves, they are quite special, the outer plate rotates around so you can fill the chamber to the left or the chamber to the right, or both or none. Basically I discovered this by rotating it round until I found the position and thus the option I was looking for. Its also a pressure release valve for both chambers.
The central valve can be unscrewed and you can the ports in the outer valve, if you have it set to blank it all you remove the stress on the initial valve and you can then take it out and clean it. All mine needed was a clean to remove 10 years of seismic survey abuse - washing up liquid and water, I was hunting for leaks at the time
It is possible to set all the valves to make it into one giant chamber then attach the air line and it all comes up in one go, but you must remember to reset it back to either one chamber or none for safety.
From rereading your post and knowing how hot its gets in Auckland this time of year it might just be the over pressure kicking in, due to the black tubes, I got this a bit in the UK in summer.
As for a full strip down I was never able to get that info off Zodiac either.
one thing I did find was that the valves for the futura runners being plastic threads it was easy to cross thread and damage and cleaning out under the deck was important to minimise wear even though it was a sod. The non return valves for the bilge are not spectacular but we just learnt to live with it . Somewhere I have a line drawing of the hull but no manual for it if thats any use pm me.