That's interesting, something to consider - what seals are these in the rear struts?when struts and or rear suspension units get old there seals may not hold mains system presure,
so this can cause the car to sink quickly after engine off,
I rebuilt the doseur on my yellow break and it stays up longer than before but only for 2-3 hours max. One of the seals is no longer available so I used a Viton seal that was the same diameter but ever so slightly smaller in width - perhaps a factor? The brakes are ferocious now though!