It's very hot and humid here, and I give the brakes a good workout through the tight steep corners around and through the hinterlands.
I was mostly wondering how the deterioration takes place, will they slowly become spongy.
That spec looks to be valid for heat load from race application carbon/carbon near through to glowing.
My assumption is that the chemistry is stable to way beyond what your parameters could ever introduce in terms of heat load transmitted to the fluid.
In other words, I don't see how heat induced chemical decomposition or any kind of "morphing" would be possible.
Water ingress from hygroscopic effect though, will degrade it and the result is boiling point suppression.
And one can't visually tell any water has gone into solution. (unless the fluid has something in it to make it change colour from the presence of water, like Castrol Girling Green used to, any water in it made it turn blue).
Beginning stages is sponginess, then worse, then total loss of actuation.
(had it happen to me in a car once, total loss that is, not fun at all!)