Re: I think my gearbox has gone.....
I'd venture to suggest that if the car drove OK under test drive before you bought it, then you might simply have been damned unlucky as what happens sounds like a breakage, which you can't really lay at the door of the previous owner, no matter how much one might like to curse him.
I'd get an ebay gearbox or speak to Richard Murtha (of this forum) or any other reputable Alfa breaker.
Its going to be a financial hit whatever you do, but i'd always try and investigate fixing the car first and foremost. I'm not a selespeed fan..solely on reliability grounds, but there are those who have had good service from them, and I'd have quite liked one had they been more dependable.
Very sorry to hear your first Alfa experience has been a bad one.
Whereabouts are you, by the way. Your profile is a little thin