Hi Jon,
I understand this description/theory (I think).
Thanks for that although I must say that in my 35yrs motor trade experience I have not come across these characteristics before - I'll be testing this theory in every diesel car from now on, in fact I tried this today in a Citroen Picasso Diesel and guess what - no sinking brake pedal!
But this pedal sinks regardless of whether there have been 2, 3 or no previous brake applications.

Colin