Had my car serviced 3 times by Alfa dealers. On the last service I was told the sump nut had threaded but they had managed to get it "tight."
Decided to service the damn thing myself and low and behold.
It seems like the oil filter has never been removed, because the undertray fixings were seized (had to grind them off), which makes it almost impossible to replace the filter on a 2.0. Also someone had cut out the tray around the sump nut (to make it accessible without removing the tray I assume). LAzy b*stards.
On removing the sump nut I tried to retighten the nut, was only really finger tight. The next day the was a small pool of oil under the car. Had a chat with a mechanic and ordered an M18 * 1.5 * 11mm wire insert (got 10) plus the tap and screw insert. The total cost was £60.90 inc Vat company is www.wireinserts.com
, very helpful, needless to say no more leaks. According to ebspares most people replace the sump, and it is a common fault as the sump is alloy wheras the bolt is steel, one shrinks the other doesn't.
Hope this helps if someone is unfortunate enough for it to happen to them. Fitting the thread took 5 minutes.