I had the same issue with my old D2. I agree with changing the air bags as mine only leaked at a specific hight.

Although what I did do was put half a bottle of "Slime" tyre repair fluid in the bags and had no more problems for another 2 years until I got around to changing them out.

Dodgy I know but it worked a treat. I just undid the air line and then took out the fitting and squirted it in. You have to jack the back of the car up to get to the fittings or take the wheels off.