I can't tell you which oil to use because I don't switch around and take oil samples to see how things are wearing however for what it's worth I've used Shell Rotella15-40 in my semi and have no unusual wear areas or leaks. I would try to stick to one type of oil/weight as much as possible becuase there are slight differences and you want the motor to wear evenly. I think as long as you use a quality name brand oil and change your fluids often you'll be fine. The fuel you use also plays a part in the lubricity of the injectors and cylinder walls as diesels have high compression and alot of blow-by. Use quality fuel from reliable fueling stations because as diesel settles it starts to seperate and the lubricity of the fuel will change. Two things that shorten the life of a diesel motor is driver controlled. Lugging a diesel motor with all that high compression will wear out your bearings quicker, and make your oil dirtier quicker becuase the exploded gases will be wasted as blow-by instead of doing useful work of turning the crank. Second, running high RPM's will shorten the turbo and flatten out the cams at a quicker rate. Good luck and sorry about the weaping SVX. If a seal has a chance of leaking synthetic oils will let you know. On the bright side Sythentics clean up easier
