Check the F connector at the motor end of the short cable from the LNB.
These often come loose with repeated panning of the arc ............... when the dish moves one way it pulls on the cable a little, and when it moves t'other way, the connection cannot fully re-tighten.
This gradually gets worse until you lose your channels.
Easily solved by restraining the cable a few inches from the connection, by strapping it to the mount. ie You shift the fulcrum from the connector itself.