2 years ago I bought my 156 deisel at 4 years old and 100,000km for 7,000 Euros in a private sale (ie, no warranty) plus the cost of a full service (incl cam belt) and 2 new tyres.
Since then I have done 60,000 km in it, mostly motorway but also shooting the traffic through Brussels each day. I must admit that it has let me down twice. Once teh MAF (I think) went and the engine stopped. 2 days and 125 Euros fixed that. A year later the starter motor started acting up. Had it changed out for 200 Euros and that's all good now.
I have been unable to find a fully equipped indy alfa mechanic in Belgium (anyone...?) so I wince and pay the main dealer prices for services, which are not cheap. I have to say, though, that they have done a bang up job of keeping it on the road and can keep the computer on the straight and narrow...most of the time
Despite some small niggles and the not insubstantial servicing costs, which you would be able to mitigate by finding an independant mechanic, which there are lots of in the UK anyway I don't regret my purchase in the least. This is not an appliance, it's a car and a damn fine one at that. I'll almost certainly trade up to a 159 when the 156 hits 200k in a year or so.