Linear Actuator of the boom of 42006 jams
First off, you should check the instructions to see if you made a mistake before going into some long repair method. Even if you find no mistake, what I would do is disassemble the entire crane assembly and then reassemble it; this would fix problems you may not have noticed. Another thing you could do is remove the actuator and fully extend and retract it a couple of times. If you feel any extra friction while doing this, than the actuator might need lubrication.