Selling up soon :(
Join Date: Oct 2005
If you can pick up a 2nd hand gearbox for €300, its cheaper and quicker than splitting the box open, finding out whats wrong, ordering in parts and fitting again.
The crack i assume is visible at the moment, so it wouldnt be the slave cylinder which fits between the gearbox and engine. If its leaked oil and having major issues as you suggest, lots could be wrong inside and could have put untold stress on other parts which could break in the future due to running with a lack of oil. Best to replace in full.
Alfa's are pretty unique and I have learned even trusted mechanics struggle with these cars and can make mistakes. I take the car to a specialist if its anything mroe than routine servicing.
As for the clutch, has it ever been changed before? If not, he has made the right call to replace it. You would be due a clutch change anyway (normally) within the next 20k miles, you might as well do it now, while the engine and gearbox are out, than paying again in maybe 6 months to have the gearbox taken off.