Very interesting; did you pressure test any of them? My Xantia fronts ("urepan" multilayer because we are one of those pays chauds by PSA standards) are a shade over 10% depressurised now compared to spec.
I'm a little put out, that a new pair of genuine multilayer spheres to suit, is $480 here. Because my car cops a hiding and gets quite hot, I am skeptical of the merits in using anything less than a laminated membrane sphere...