Re: oil consumption

Excuse moi, je ne parle pas francais..

Looks pretty much like there is some serious problem ahead with your engine. Even without valve guide seals the engine will not burn 5 Liters oil per 1000km, as your engine does.
Black or dark smoke while flatout, even at high revs, is just overriched mixture, not oil.
You should check spark plugs at first, then check compression, I guess one of the pistons is gone.

just my opinion, maybe I´m wrong, but I´m afraid not.....

kind regards

Roland