Thanks guys. Talked also to the Main Importer Technician today on phone and he told me two things.
First: The gasket is obviously stuck to the cylinder head and therefore easily overlooked by Noobs, otherwise if there were no gasket, it could be heard easily. Louder Engine/Exhaust Noise.
Second: The gasket does not necessarily have to be replaced with a new one each time the pipe was removed.
So, obviously I´ve just overlooked my gasket and there is one also on my scooter. :-) Engine Sound is normal.
But I´ll also get one or two new gaskets as spare parts and will change it at the next rear tyre change. :-)
Sounds good, doesn´t it. :-)