Paul,

Hard to speculate without having them in front of you.... but you may want to check the nylon spacer that goes between the frame rails at the back side of the retract unit. This spacer acts as a stop... thus has a flat ground on one side of it.

Sometimes the screws will loosen in the retract unit and the spacer will rotate slightly. If you look you will see that the spacer has a flat on it. This flat should coincide with the flat on the back side of the pivot block in the extended position.