Caps are hard to confirm by eye whether they;re legit or not, as long as the voltage and temp ratings are correct they should work ok.
Threadlock won't do much seeing how they put it on the heads at the board, you need to put threadlock on the threads before you screw it in. The screws were already loose even before they put threadlock on them it seems.
Those aluminum pieces sandwiched between the amp IC and heatsink helps to spread the heat better. It simulates a thicker substrate in cases where manufacturing thicker heatsinks can be costly. Refer to a Naim NAP200 for example. The output transistors are heatsinked to the floor of the amp, but there's an aluminum slab sandwiched between them to spread the heat. In the following image you can just about make out the aluminum slab underneath the transistors

Usually the sandwiched pieces are bigger, they must be saving up a lot of production cost lol.