Our 365GL was purchased end 2006. It was fitted with a poor gear lever which I am reasonable sure was supplied by Plastimo. The handle was prone to fall off. Within a few years, I got so frustrated with it that I fitted a Volvo gear lever which has served us very well ever since.
Bob’s comment above about pushing in the grey button should enable you to better understand what is the issue. It could be the gear lever or a kink or bad bend in the cable or even something causing an issue with the lever alongside the actual gearbox.
Hope this helps. Chris