Originally Posted by Sid Squid

Lift the tank and you'll see the adjuster screw that the flexible drive turns. If the screw gets stuck the drive, being flexible, often just winds up rather than turning it.
Squirt some oil or whatever on the threads of the screw, and using a pair of pliers carefully grip the screw by the plain section where the flexible drive meets it, once you've got it moving try to get some oil into the threads on the mount.