Thanks all for your good advice!
Actually, the old pan was also mounted with liquid seal, and it ALSO leaked like crazy, and the leak is clearly from the lower pan, as the engine is dry above this point.
In the autumn, when I had to change the oil, I bought a new lower pan (costs like nothing, 30-40 EUR), and then a new cork seal for the oil pan. My mechanic mounted it and carefully removed ALL of the old liquid seal, which he really hated (!!), and initially it only leaked a little from the new cork seal, but it has gotten worse, now when I have started driving the car after the winter, and this was the reason, why I asked for the torque levels.
But I now re-torqued all the lower pan bolts with 10.8 Nm (=1.1 kpm), and actually ALL of them needed torqueing! HOWEVER, it still leaks like crazy, when the oil has been up at normal operating temperature (when driving for more than 20 min), and I use normal classic 20W50 mineral oil (from Duckhams).
It is really irritating that everywhere I go with the car, I am ruining someone's pavement with all this oil dripping from my car. And it is embarrising to having to place a cardboard under the car, every time I stop!
So, should I just torque the pan screws even more than the 10.8 Nm? If so, how much?
Cheers,
Christian