how can i fix my mercedes a140 tiptronic clutch control unit?

I have been getting an intermittent fault on the cluch. the F symbol comes up on the gear indicator and it wont let you start. took it to the local car electrical epople and they said it was intermittent fault with the clutch control unit, probably not the actuator, as when it was working , the clutch seems fine. they did say that the control box looked pitted, and that the labour for them to look at it would be highly expensive (honest of them!) so I need to sort this myself... any one else ahd this issue and fixed it?
Oliver