The metal hood is held onto two springs and a height adjuster knob which you remove by taking a screw out, not a huge fan of the design which is why I'd recommend the SC688B. Or if you want a better motor, that's where the Bissell Big Green BG101H comes in cause they still use metal motors.
The X4 doesn't need to have a gasket in the bag because there's already a rubber seal in the internal cover. The way the bag works is there's a lever inside the bag door. If you open the bag door latch up, the lever pulls the bag down from the internal cover. And if you close the latch down, the lever pushes the bag up to the internal cover. It's designed that way because it makes changing the bag alot easier. Also what's so cool about the X4 is if you try to put the cover back on without a bag inside, it's not going to shut properly alerting the user that there's no bag inside. Same goes if you don't have a microfilter inside, it won't shut the cover for you either. If you hadn't seen that from the X4 review video I shared yesterday, I invite you to do so. It's 40 minutes long but it basically covers everything you'd need to know about the machine. The motor is brushed but the brushes are replaceable, this is from my X5 that I dismantled for refurbishment to give you an idea of what's inside. It's the same thing as the X4 but the brushroll is wider. They don't make those models anymore but they do make an X8 that's similar with a few improvements.