Congrats, looks very special and I admire your courage picking up the car after such a long flight/day and driving another 700 km in it in such bad weather on semi-slicks. Even I wouldn't have been that crazy.

4.0 bar? Ouch. No wonder. Dealer is an idiot, sorry to say that. Happened to me as well (not 4.0 bar but dealer always tends to put the "comfort" tire pressure instead of the normal one, so I always end up getting a tire pressure warning once I pass 270 kph). Tire pressures are no joke, dealerships should be much more careful about them.
Well, you got to Bruxelles in one piece, just another adventure, remember the good moments.
Enjoy and drive safely, the new GT3 is an amazing car. 
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RC (Germany) - Rennteam Editor Porsche 991.2 Carrera GTS Cabriolet (2018), Porsche Cayenne S Diesel (2017), Audi R8 V10 Plus (2016), Mini JCW (2015)