Phil, great choice of car
I am far from an expert on these things, but I have had mine for 7 months and 13k miles so far. If it were me, I would look at the following:
- Listen to the engine, should be near silent. No tappety/valve train noise to speak of.
- Check the oil level. Mine uses a litre every 4k miles (not uncommon) and if the previous owner never checked it, may be problems later on.
- The rear suspension seems to get tired early on with the 166. Mine was shot after 50k miles, and Alfa want £800 to replace springs/shocks. Sometime in (I think) 2000 or 2001, the cars came with VDC - vehicle dynamic control - and the general consensus seems to be that the suspension is much better on these cars.
- Mileage. The 60k and 72k services are expensive, just bear that in mind.
Other than that, cannot recommend them highly enough. Wonderful, wonderful car. I am heavily biased against the 4 speed auto version, but even the manual drinks fuel like it is going out of fashion. Slight downsides on mine...., it eats sidelight bulbs pretty regularly, the clutch system has some sort of hydraulic leak somewhere that the Alfa dealer is struggling to find, and it wears the rear tyres quicker than I expected. I think that this last one is related to the soft suspension.
Good luck with your search, great car. No more expensive (to buy 2nd hand) than a V6 156 either.
Do feel free to ask any further specific questions, it is always good to hear from another 166 owner.