This happened to me with the GSA. I was topping up regularly for a while because of a leak from the rear - the LHM was always clean...
Until one day I topped up one morning (with engine oil actually), set off, then after about 10 minutes driving the STOP light came on *again*...
... got caught in traffic heading through Guildford, and started to get that sinking feeling...
Pulled into a local ARE motorfactor... bought bottles of LHM, poured them in, started up, then watched a huge puddle well out from underneath.
Turns out the rear n/s cylinder had failed - the rubber part had split and LHM was gushing out past the piston. What I *didn't* know at that point was if I'd put the car into intermediate position it would have held most if not all of its fluid. It was the flexing of the rear suspension in normal height that was pushing the fluid out... at the higher height (as I found later), the piston operated in an intact portion of the cylinder). The car would sit quite happily in high position losing no fluid whatsoever...
So, not knowing this, I ordered a flat-bed truck and the poor G had to be dragged onto it sitting on its bumpstops..., using wooden ramps in order to prevent the exhaust hitting the ground on the way up onto the truck.
After it had languished on my drive for months with a roasting tin underneath to catch the fluid (I started it up every so often and put it into high - but fluid was inevitably lost as it eventually sunk down) , I was able to drive it all the way from Woking to Chevronic Centre in Bedfordshire in intermediate height without getting into difficulty!!
Good luck with your BX!
Mark.
