If you think we have problems...

[White Exec]

With the system sealed, stress on the tank is continual all the time the car is being driven (suspension movement) and also after it has been parked up (thermal effects, and less-than-perfect anti-sink). You are right about the tank needing to be strong, and maybe the material which it is made from has turned out to be not the best, although Citroen appear not to have changed it. The only 'cushioning' in a sealed system is the air space above the reservoir fluid, which equals pressure.

While DOT4/5 brake fluid is highly hygroscopic, I suspect that LHM and LDS are far less so.

You're probably right about the effect of a sealed (= pressurised) tank on air ingress between reservoir and pump. Hopefully a leak here will show up as just that - a leak of fluid, rather than the suction situation we have on ours.

Not the first time Cit have got plastic tanks wrong. Seems Xantia coolant tanks go pop regularly, too. Nothing wrong with plastic - just needs to be of the right type and thickness.

[Dieselman]

It's the welded joint of the two halves that fractures, indicating a manufacturiung weakness, which goes undetected until the joint is under contatnt pressure and thermal cycles.

I'm not sure whether LDS is hygroscopic, but possibly so, much like the original vegetable oil in early DS, which caused many failures. Vegetable oil ester amy be being used again as it is good for drawing water away from brake caliper seals and pistons, to reduce the incidence of seizure due to corrosion.

What is the change period recommendation on LDS?

I suspec the tank pressurisation is to aid pump priming as it is a sealed sytem...and because electric pumps are rather poor. Ask any owner of a Mercedes with ABC or air suspension... ABC is Mercedes version of Hydracive3 with added body control and thousands of times less reliable.

[White Exec]

LDS is, apparently, simply a synthetic version of LHM, and with similar hydraulic properties and viscosity.
Not sure about hygroscopicity - the Total sheet doesn't seem to detail this.

[Dieselman]

If it's synthetic, I suspect that is unlikely.

Vegetable esters tend to cause system corrosion and attack nitrile rubber seals, which is why Citroen went for mineral LHM. As already said, Esters do draw moisture...but who changes their brake fluid religeously every two years...apart from me...?

[Dean]

I do. but im sad too Will

D

[Dieselman]

I'd rather change brake fluid than a master cyclinder or seized caliper.

I've got all the High-tech kit to do it, so why not...