Leaking oil / possible high pressure in oil pan.

Hi everyone!
I keep having this problem since I bought this car.
Car was used and it had a hole in the noise dampening foam right above the oil refill cork (pics).
In the back of the engine, next to exhaust there is one, in my case rusted cover closing some outlet. This rusted part has a gasket that keeps leaking.
Usually the leak happens when the oil is overfilled (toyota dealer did this to me) or I aggressively step on the gas couple of times.
This time the leak happened after a long trip (2600km). The trip involved high speed, around 180km/h.
After this trip I saw a tiny leak near the rusted part but the whole oil was gone! Around 4L just gone.
I didn't see any areas that 4L of oil could have just poured out so I guess it was burned.
I had compression test done and all is good, unfortunately Toyota in my are is incompetent and they don't care what information the customer gives so they did not investigate the 4L gone.
I also found something greased up on the top of the engine, I have no idea what it is.

Any ideas?

General area of the problem:

Closeup of the area. Sorry for vertical ...

 

That was my suspect too. I would love to buy one and do it myself but I live in Luxembourg, Europe and it's almost impossible for some reason to get this part. I will have to get it from Toyota.

 

Car has 221000KM (137000 miles).
What's "short fill"? I'm not native English so I don't know if I understand it correctly. Is it when you put not enough oil? Because before every bigger trip I check the usual fluids and so on. Oil was at the "top dot".

 

The "oil pressure switch" is the PCV, right? I'm not native English so I need to make sure on some things.
In regards of speed, the rating on the car is up to 180km/h. I saw on the net people going 210km/h. In my opinion it should not burn oil as it was petrol.

 

I saw the video that's why I think I can do it myself.
I got a medium threadlock so I'll reapply.
We'll see on the weekend.

I would also like to say thank you!
Whenever I have a question you always try to help so thank you again.

 

Hi again.
The rusty plate is in fact the chain tensioner as you said.

Due to some "miss comunication" the pcv valve was not changed. They checked the chain as I asked and resealed the "rusty plate".
I am now supposed to drive around, monitor the oil level and go back to Toyota in 1000km.
After all this oil leak/burn my consumption went up.
I was getting 4.4L/100km (~53mpg), now it's 5.6L/100km (~42mpg).
I do have new tires but during my trip, in city I managed to get the normal for me, 4.4L/100km so I don't know what's going on really.

 

Summary time!
Oil just dissapeared (got burned). After driving a lot, the car is not burning oil anymore.
That means the car will eat oil like crazy when doing almost top speed for 2-3 hours.
I also found out that if you'll go top speed for 2-3 hours it will just butcher the battery. Capacity of my battery took a horrible hit to the point that I'm thinking of replacing it. No yellow triangle yet.
So ... be aware!