The soft MC problem has always confused me. Perhaps someone with more (admittedly mine is very minimal) knowledge of fluid/hydaulic/flow dynamics can clarify.
The MC is located approx. 10ft from the hottest constant source, engine compartment; air anywhere in the system will give a mushy pedal, and it seems logical that the fluid would be the hottest (boiling out air?) in the engine compartment, or secondarily in the caliper regions when severely using the brakes. So wouldn't the slave cylinder be more of a concern? Or simply the heat in the engine compartment is too great at times for the fluid to accomodate?
Most who have raced cars know how often brakes get mushy as car gets hotter, and a part of prep was always bleeding calipers frequently since this was where the air was; pedal firmed up and out we went for next session. The MC hadn't failed.......
The fluid doesn't really flow when brakes applied, so it would seem difficult to generate such a high temp in the MC itself, so far removed from high heat source? Would seem if MC is the culprit, it is so because of poor design/manufacture that fails to seal properly under pressure. If so, failure should occur at any time not just when car is used heavily and high heat is generated?
This is why I asked for info on the 400 MC performance, since 400 has same part # (see "Evora 400 Problem" thread). Anyhow, just scratching my head.........
A number of good points. You are correct that the MC is in a relatively cool position.
While the Brakes and Clutch share hydraulic fluid, this sharing is on the non pressurized reserve side, so hot fluid from one will not actually migrate to the other.
Be it brakes or clutch system, the fluid does 'flow' rather than just transmit a pressure pulse, the flow is not continual though but rather a 'tidal' back and forth by the amount of volume change under the piston and as the line diameters are very small ... I estimate fluid moves about 3 to 4 feet each way in the clutch line with pedal movement.
Boiling fluid in the system with air will create a vapor pocket, system is sealed so air does not just boil away, gas bubbles will work up to 'higher' ground, that is the MC as its above the SC; maybe its those that do the MC in???
I never had an issue with my S1 car and after recall to add insulation I added an extra layer full length from SC to the Damper, I never understood the factory additionally of only a few inches at the SC side. My 410 had not exhibited any issues at 7500 miles and to day I have not added insulation other than the now standard factory partial wrap. I do have an Tilton/BOE MC at the ready on my home office shelf, just in case.