Hi Karel,
I've been pondering how to test the anti-sink sphere and this may work:
Given that the sphere provides a reserve of pressure for the rear brakes with the rear anti-sink valve closed, if the sphere is good, the rear brakes should be able to be applied a few times until it is exhausted.
Raise the rear on axle-stands, start up, set on high, allow full normal pressure to be achieved. Stop the car and wait for the rear anti-sink valve to come into operation as main pressure falls and then see if the rear brakes can be applied. If the rear brakes are able to be applied a few times, the anti-sink sphere must be supplying at least some pressure.
This is all a bit of guesswork but accidentially I think I have made use of this property of the anti-sink sphere when bleeding my rear brakes
As for the disassembly of the anti-sink valve, it must be possible as every other hydraulic component can be dismantled fairly readily with care. The valve is a high-recision component and will need dismantling under clinical conditions.
What does your LHM look like? If it is old and brownish, the valve could be sticking and thus a hydraflush will be highly recommended to clean everything up and maybe free off the valve without needing to dismantle it. It can work wonders for lazy height correctors
and it takes about one minute in the morning to rise. The car begann to sink suddenly, from one day to another. The front stays up as usually. Both height correctors work fine, there is no LHM leak in the whole system. Have plain hydraulics with 6 spheres, no hydractive. The four suspension spheres on all wheels are also fine. 