Timbo
As you have series II disco, it has ACE suspension.
Does it 'lean' all the time, or only when parked ?
I also have an occasional 'lean' depending on where I park.
When I park facing the house it sometimes 'leans' to the nearside
If I park facing the other way it sometimes 'leans' to the offside.
This is because the ACe is trying to level the car, but has the power switched off.
If yours allways leans to the same side then it is probably a leaking ACE unit.
rgds
Derek