Thank you very much to all of you, for your very kind comments, and for your warm welcome !
It is intersting to mention that this car had a special feature, unknown in other examples :
Behind the driver's seat, a device was fitted, enabling a 3-position adjustment of the seat back. I have not been able to determine whether this was an "after-market", private modification, or a special bespoke feature requested by a client.
The mechanism seems both simple, effective and of professional quality. To me, this device looks like it was designed by the factory and could have been considered for implementation as a standard feature, or as an option, on the S1, but possibly rejected for cost reasons in the end. It still is a mystery for me. Maybe someone has seen this on another S1 ?
The system is quite smart (please excuse my clumsy wording, english not being my mother tongue) : a simple steel wire formed as a loop can be pulled to move a bracket back and forth (thanks to a spring) and therefore engaged into one of three holes. Depending on which hole is selected, the seat back is blocked more or less forward, enabling shorter people like me to drive more comfortably, with upper body closer to the steering wheel.
