Do a search for more info but mine has the same problem, can go for weeks/months with no problem and then suddenly in matter of ten mins or over night rear left drops to lowest, normally happens when ive parked on unlevel ground especially if front higher than back, i know what my problem is though it will be a fine hole in the air bag, search on here and you will see the best thing to do is to cover the air bags in soapy water and look for blowing bubbles, do this to all the pipes as well, replacement bags are about £60- £80 each and Im told its easy to do your self as long as bolts come off, again its all on here somewhere, and some one will put us both right coz they are all dead clever chaps and chappesses.Happy New Year all !!