What is the most likely cause of a pump action cocking malfunction?

A broken sear is indeed a likely cause of a pump action cocking malfunction. The sear plays a crucial role in the firearm's firing mechanism by holding the hammer or firing pin in its cocked position until the trigger is pulled. If the sear is broken, it may fail to engage properly, causing the action to not function as intended when the pump is cycled. This can result in the inability to cock the mechanism, leading to a malfunction in the process of preparing the firearm to fire.

Understanding the role of each component can help to identify that while other parts like the trigger, extractor, and bolt are important for the overall operation of the firearm, the sear specifically has a direct impact on the cocking function. A damaged trigger might affect the ability to release the hammer but wouldn't necessarily prevent the cocking action itself. A faulty extractor could cause issues with ejection or feeding of cartridges, and a worn bolt might impact overall cycling but wouldn’t directly prevent the hammer from being held in the cocked position. Therefore, the broken sear stands out as the most probable cause of a cocking malfunction in a pump action firearm.