Had the same problem with mine last week, the ACE block was leaking from the rear.
Ended up getting a lift home with the AA it was loosing so much fluid
First off check your pipes for corrosion , if they are ok thats good cos the front pipes are a bast*rd to do as they are fitted before the body at the factory and the new ones come in 2 parts.
Mine turned out to be a blown seal cheap fix really and easy to do too..
First off as mentioned before KEEP IT CLEAN then take a look at this link
Discovery Owners Club :: Tech - Active Cornering Enhancement and scroll down to the valve block section.. there you will see how the seals work..
Two choices now the cheap one or the relatively cheap one
Cheap option : undo the two nut that hold the pipes on an gently pull the pipes out, once out of the way cover them up so no sh*te will get in the system. Then using a 10mm bolt ( clean new one ) screw this in to the valve block seal and extract the seal (you will probable need a pair of mole grips and a hammer) once out you will find the o-rings are shot replace and rebuild in the correct order as shown in the above link (just take care and your time when inserting the parts so they seat correctly also note the depth of the plastic part you may need to tap it in slightly using a socket to get it right)
Second option : buy the complete seals from Land Rover part no RVW100010, think they are about £14 each so not to bad if its only one or two. they come ready to fit on an applicator so no messing about like the first option
My fix used the cheap option so only cost pence to fix not bad considering i had the same sort of silly quotes as you did
Good luck
Also you are supposed to get the system bleed if you disturb the pipes, me being cheap thought sod that and took it slaloming down a quiet road only took a few goes to get it all working again lol....