1 hour ago, Shearers said:

As far as I can see it is a thin, flexible diaphragm that can move as the fluid level changes:

For the Fluid level to change then something needs to replace the space that the Fluid took up and that is Air, which has a Relative Humidity of anything up to 100%, I've just checked on the BBC Weather App and it is 77% here at the moment, that's why the Fluid gets contaminated with water even when there are no leaks and the Cap has never been off.

If you don't believe me open a Bleed Nipple,. Fluid will slowly leak if you do, it might take a while. If you now manage to seal where the Cap fits the Fluid loss will stop unless there is a leak somewhere else as per my earlier post about changing Pipes where there was no Flexible Hose to clamp.

Well it's booked in for middle of next month for 2yr scheduled service which includes getting the breakdown cover and making use of the Ford £30 off deal. It's 4 weeks early going off date of first collection (SEP 2023) so out of interest does anybody think I've gone too early ? Engine build was May 23 so obviously oil probably sitting since then anyway.

5 minutes ago, MCF said:

...so out of interest does anybody think I've gone too early?

No.  Next year it'll be good to get the MOT done a month early just in case anything needs doing for that.

Firstly because it means you won't end up driving with no MOT after 3 years old.  And secondly because if anything does fail MOT then the car will still be under manufacturers warranty at the time.  We would like to hope Ford would offer 'goodwill' for a week or so out of warranty, but there's no risk if it's still within the 3 years.

2 yr 18000 mile service completed at dealer. No mention of brake fluid and all good. £286 including 1 years AA breakdown cover and completed while I waited.