my 2004 110 had a cracked brake servo few weeks back , now having checked a couple of friends defenders they had the same problem. have a look either side of where the master cylinder bolts to the servo for cracks, mine had a tiny crack and spraying wd40 on it you could watch is being sucked in the crack, my friends td5 90 last night was so bad you could hear it sucking air. the same servo is fitted to 200/300/td5
