what replacement parts/issues are usually present on a G35 thats got 100,000 to 120,000km on it? Saw a couple of craigslist they are 2003 and 2004 cars.

Kluk, high mileage isn't a bad thing if the G35 has been taken care of. If not, consider the fact that nothing for a Infiniti G35 comes cheap. You're better off finding a low mileage car that's been pampered and has all the service records regardless of the year!
Gary

You will probaly need to change the compression rods, that's a known problem.