The manuals for the BMW's sold in Europe say that you can substitute LHM for CHF-11, which I have done. LHM is Citroen hydraulic oil. In the US many Citroen owners use MIL 5606 red hydraulic fluid used in light aircraft, snow plows and other hydraulic systems. It has a slightly lower viscosity, so if you have a leak it will make it worse, but it is readily available and cheap.