well ok, i think you guys are a bit biast, so am I.
The gearbox are dam strong, but synchros suck.
Stock clutch will need an upgrade at 200 rwKw.
The S2 Turbo i find is great, it has lived at 15 psi for ages, and no issues, pulled 217 rwKw. It's all in the tunning.
THEY GUZZLE FUEL, i have been in 5 different ones, and they all eat fuel.
Unless you can do a lot of things yourself, they will be expensive for others to fix, they tend to have expensive genuine compopnents, so unless you do the leg work yourself, your up for big bucks.
EXHAUST MANIFOLD, i have not found a skyline yet, that has not had number 1 and 6 manifold snapped off.
S1 Interior scratches up SOOOOOOOOO easily.
The carpets will get holes in then in a day if cheep carpet matts are used
Other then that, these cars ar up to 13 years old, so thta means that all will have some issues. BUT buy wise and you will be ok.