There doesn't seem to be any reliablility issues with these bikes. if i remember right, there is a guy i LA with over 80k on his, and i don't think he's had the motor opened. More important is the care that has been taken in maintaining it. look for the obvious tell tale signs, such as brake pads, chain and sprockets, and cleanliness of the whole unit, not just the shiny parts!
Valves are called for at 16k. many of us, upon hitting that mark, simply checked them, found them within specs, and put it back together
These things are bulletproof!
The 919 was relatively unchanged through it's lifespan, the most noticeable change i can think of besides color being the addition of adjustable compression dampening in the forks for 2004 (it may have been 03, i can't remember off hand).
we're looking forward to having another niner on the roads, and in the forum! hope you have fun, and don't be a stranger around here!
(what kind of bikes are you selling? i kinda want an older interceptor...)