Sometimes there are a few spots on the driveway beneath the vehicle. I tried to locate a leak and let the engine run for 20min on the spot, without any oil coming out. It doesn't consume more oil than it did before (a little sip every 5000km).
I will look into the changing of the timing chain. Eleanor is due to inspection next week so I will ask my mech about it, too.
The V6 engine was replaced by the current 4Y-E by the previous owner about 14000km (~9000miles) ago for consumption reasons.
It seems to be a very common thing here in Australia (so my mech) and the 4Y-E engine is also described in my owner's manual.
To prevent sludge formation, I use the
Nulon 40-70 extra thick oil (Aussi brand, I guess).
Thanks for your replies so far!