Hello,
Around 1969, US DOT required all US delivery vehicles to have safer, soft dash knobs. The USA 113 delivery cars got new heater levers with rubber-like ends from the factory. Unfortunately sun and ozone degrade this material making it brittle. Often times it just crumbles apart for no apparent reason. Jambed or stiff heater contrlos aggrivate the problem by adding more strain to the assembly. Replacememt of the original levers is expensive and time consuming. The Duro Levers are a less expensive repair and can be replaced in as little as an hour. They do look different and the inner acrylic parts of the lever must be in good shape for them to work. If you have some stuck heater valves or cables, this must be cleared up also. The original levers in contrast may take a novice a couple of days to replace. A experienced technician can accomplish the task in a few hours or more.
My favorite levers for the 113 are the pre 1969 also all euro delivery 113s. They were solid acrylic with a tiny pop-on endpiece. They do not degrade or break like the rubber units. They illuminate much nicer being mostly acrylic also. The pre 1969 or euro W108 sedans used very similar "acrylic" levers which fit 113 cars.
Joe Alexander
Blacklick, Ohio