The first video shows the assembly, it moves quickly so be ready to pause at areas of interest. The sear isn't assembled in this video, but it's disassembled in the second video, which shows the correct orientation of the sear spring, which is easiest inserted from the rear/dull side of the sear, with the shorter spring tail on the dull side, where then the sear pin with disconnect spring (note its orientation) can be inserted.

However, don't take apart the sear unless needed, it's tricky to reassemble, requiring a deft touch and appropriate size punch with which to use as a follower for the reinsertion of the disconnect pin. 

The second video shows the disassembly, wherein we see the correct orientation of the sear spring. However, he decocks the hammer which should NEVER be done unless you're prepared to reset the hammer strut and trigger spring, as well as bending the hammer strut. See in both videos that the hammer strut is slightly bent, which the author seems to think is normal. Thus, I suggest using duck tape to securely tape down the hammer whenever the slide is removed.  

The author isn't a very good mechanic in my opinion, he uses hasty tools and some shady methods, but the videos show things like the sear and magazine spring orientations, which might not otherwise be known by looking at the pistol when assembled, particularly the sear spring. And this thing with the hammer coming forward, which not only bends the hammer spring, but freezes the hammer into position thus requiring it's removal and reassembly, such a design flaw shows a hatred for the customer. I honestly feel that (the old) AMT's owner and designers should be jailed for a thirty years, which is collectively the amount of time that AMT's customers have spent trying to get their pistols to function properly.