ride height sensor calibration

Hi all my disco is listing on near side and i the same with or without engine running. I have checked all connections and air springs for leaks but none found, so i'm thinking must be ride height sensor. Do i have to take to dealers to re calibrate or can i buy something to do it myself. Cheers all Mark

This seem to be a common problem according to the forums, I understand they, the sensor arm, sticks because of mud etc so it lacks the full movement so have a look at that, also this link may help you.
http://www.landyzone.co.uk/lz/f38/disco-ii-air-suspension-definitive-guide-61211.html