Watch out, it looks like they are desperate to sell that can of oil to you...
Browse around on the forums and go to mechbox.com for some vids. I was unlucky to have my mechbox break, and therefore HAD to open it up. once you understand what actually goes on inside the mechbox, it's quite simple. Just requires a bit of patience. For inside the mechbox you will want to use a high quality silicone-based grease, such as Super Lube. But you don't need a ton of it. I don't think I even used any of the oil for the whole job. The oil is more what you use for GBB's and sticky mags.
check out the videos on mechbox.com for a V3 mechbox (which is the kind used in the 552). If it were my AEG, just shim it, grease it, and just replace parts when they either break or you want to enhance performance.