458 458 spider roof problem

Hi,
For the past couple of weeks i seem to be having issues when lowering the roof down.

It always closes nice and smooth, never a fail, but lately on almost every opening, although it begins well, when center top reaches 90° it slows down, stops and suddenly, after a bang, it completes its way. Sometimes it won't go passed the bang and i have to start the process over again.
The car went to the main dealer last week for a service and they greased all of the mechanism but this hasn't helped
at all.
Has anyone had this issue before, if so what was the cause?
Thanks