Sorry to hear about your problem matey but it's not too uncommon all the info you need is here http://foc-u.co.uk/index.php?topic=92.0 and here http://foc-u.co.uk/index.php?topic=22656...#msg261329 Have a good read the latter has a copy of the tech bulletin in the thread. From what your saying you are going to need a new sprocket shaft 
come back if you've got any questions 
I'm not sure what your garage is telling you ref 17- 16mm these are easy to get hold of in the UK and the thread isn't 17mm it's 17.5mm which is also easy to obtain in the UK. I hope he isn't charging you storage? If he is I'd get your bike back and go elsewhere.
come back if you've got any questions I'm not sure what your garage is telling you ref 17- 16mm these are easy to get hold of in the UK and the thread isn't 17mm it's 17.5mm which is also easy to obtain in the UK. I hope he isn't charging you storage? If he is I'd get your bike back and go elsewhere.
Later