Hi, Just some general comments.
2500 km for 1/2 litre oil consumption. I've had cars where the manual said that 1 pint per 1000 miles is acceptable, that's roughly 3/4 l in 1600 km. The car was never that bad, but it gives an indication of "acceptable" consumption, maybe just a way around warrantee claims for high consumption.
The PCV system should have an oil separator in it, somewhere, to condense any oil vapour to stop it being sucked into the engine and burnt. If this is gunged up oil consumption goes up.
Additives. When I bought my 28 year HiAce van, with 275,000 km on the clock, the seller mentioned that it used a bit of oil. I was a bit worried about passing a roadworthy with this, because of "blowing smoke", so I added a "stop oil burning" additive to the oil. Not a drop has disappeared in 9 months. I don't know whether this is due to the additive or the seller didn't really know what she was talking about. It did use a lot of coolant, but this was due to a faulty radiator cap.
At the next oil change I will try a thicker grade of oil, say 20W 50, which is a common grade, for classic vehicles.
Herb