I was doing another DCAEK install after a couple of years and wanted a refresher. After viewing the Apex Tactical videos I came to the conclusion that they made a lot of assumptions and skipped things that I know would have been very helpful to a novice. I said to myself, "self, there has got to be a better video out there!". After searching I found two very good videos when viewed in sequence do an exceptional job of explaining and showing the process from start to finish including disassembly and assembly while installing the sear, the trigger and return spring and the USB. I know I wish I had these two videos to follow when I first did this. If the hyperlinks don't work, just copy and paste the URLs below into your browser and they will take you there.
YouTube
YouTube