To check if you have a PX old (up to 1984) or a PX Lusso gear shift paddle in front of you, simply shift to the 3 gear position. Now you can check if the sliding shoe of the shift arm protrudes 1,5mm (= PX old) or if it is flush with the sealing surface (= PX Lusso). In order to compensate for these, one uses the spacers offered here. With this it is also possible to use a PX old shift key on a PX Lusso transmission.
The PX Lusso transmissions are still used today and were also used in the Vespa T5, Cosa and LML models.