I didn't know Nissan yanked the 5-speed from the X. That sucks.
Most engineers(especially domestic) will try to say that what they make is perfect. Too bad that the engineers are under the control of cost accountants and stockholders. Visit
www.alldata.com and compare the TSBs and other issues for this family of oldsmobile/cadillac engines.
Seals leak because they crack. Too bad that the Northstar engine has cheap seals. This was common/documented with earlier Northstars and has been addressed with the newer motors.
I haven't seen a Northstar with 250k miles that didn't have issues. This is sad when you consider the market segment that the engine caters too. Older less abusive people can make almost any engine last forever. Lets see what happens to the Northstar when a 16 year old gets the keys.
Download the spreadsheet and read:
http://bill99gxe.home.mindspring.com...%20Results.zip
The spreadsheet clearly shows that certain dino oils perform extremely well and certain synthetics do too. It also shows that certain dino/blended/synth oils should be avoided. 5-7.5k is no big deal with Mobil1 or Amsoil. Even cheaper Castrol GTX dino is an excellent oil and better(opinion?) then the more expensive Castrol Syntec.
I guess that the important thing to do is to get your oil analyzed at least once, after an oil change, and then create your own maintenance schedule for your driving style, mileage interval, and your choice of oil.
I'd prefer to use as little oil as possible and will probably push to 10k intervals with remote filtration(if I ever get around to it).
Concerning xcase, front/rearends, PS, ATF, and gearboxes, using a synthetic will just about eliminate maintenance for those components. Front/rearends/manual trans/transfercases will rarely need to be changed after switching to a synth(other than for other maintenance like clutches/bearings/seals....). ATF/PS should have regular maintenance regardless of fluid choice since there is no thorough filtration.
