brotherdale - welcome to the forum
Sorry to hear about this and never heard of this before. I'd be consulting a hydraulics company for advice given the comments you have from the TIS
It's normal btw to introduce yourself on the site before diving in for repair advice.
Z4 3.0i SE Roadster (///M front, Red ///M leather seats, Aero sills, AE's, clear lenses, 4 spot rears, custom 108's, paddle shift/MFSW, quad exhaust, cf rear diffuser, Alutec strut bar, retrofit Bluetooth and a whole host of other mods subtle.)