Don't sell it mate , you will regret it
I think most of us have been in the position where we have had a problem and it has really annoyed us. Persevere and see it thru if you have virtually new everything.

It may turn out to be something small and stupid.

There's loads of good tuners and garages on here of which I have no doubt they will sort the problem for you..

Stick with it as there's not many Series ones left and it's nice to own one of the few left