Okay, I figured out that the O-rings are roll your own. It's just that MB's clever robots did it so neatly I assumed they were the real deal. However, I'm still curious how that one large 'O-ring' ended up in the oil filler section.

Also, I would appreciate knowing the name of the rear hose which attaches to the rear of the left side's small cover.

Nothing about the small covers, but I figured out that the lump in the front, upper center of the engine which looked like an electric turbocharger is an electric water-pump. Okay, I also recently discovered that there are two spark-plugs per cylinder. Do the connectors to the plugs pull off? They seem pretty determined to not let loose. Yes, I need to print out some of the available shop manuals.