2002 Alfa 156 selespeed gearbox warning light

[sebpar]

Hello
I have recently purchased a 2002 Alfa 156 from Sydney. it has 51k odometer, I had some minor works done like replaced clock spring and a general service. Drive the vehicle from Sydney to Townsville like a dream, and really fell in love with the Alfa Romeo. However Just recently I had the gearbox warning light appear, as per manual I turn vehicle off and it seem to disappear, that was about 1 month ago. This week, the vehicle is showing warning light after approx 3 km after driving. It a great concerns as I am normally on a freeway or large intersection when this happens, The turning off and on again seem to only reset itself after a few tries and then will repeat a few kilometres later.
Has anyone had this issue? know what may be causing this? and recommendation for reliable mechanic? I really like this car. Thank you in advance.