I have been working on st2's since they came out and after 98 they were pretty trouble free. 98 was a good bike but did have a few issues with its charging system, and fuel lines , and flywheels falling off. things that can be fixed.
after 98 they ha fewer problems.
the latest bikes had preload adjustable only forks. all but a few 98 bike had the same old compression valves.
All st2 and water cooled pasos are prone to warping the heads between the cylinder studs at the exhaust. It is not a huge concern but does cause it to weep oil there. Built bikes making more power are more prone to do this as well.
The ST series is the bike I should bee riding because it is a great bike , I just have not brought myself to do so. I have built and ridden st's on the track and although they are heavy they handle very well.
Anyone complaining about the headlight on a older st needs to ride an 851 or ss at night some time. Yes the ducati designs headlight is worth it.
If I were to buy an ST it would be a st2 as in new england we do not have many spaces to use the top end power of the 4 valves and the tourque on the st2 is equal or better. A 966 kitted st2 becomes a wheelie machine .
shop carefully for a good example and you will find one of motorcyclings best kept secrets.
good luck