Do the guys changing the oil not realize it is a diesel? Unless you have done the EHM (elephant hose modification, use search, read noob guide); your oil will be black. I do not know how GDE could possibly clean the oil (not why I bought it, don't see how it could) and I won't know until next year sometime (3 more changes will be almost 20 miles from now). Frankly, as long as you take any combustion gas and reroute it through the engine, your oil will pick it up. Your oil SHOULD be so black (and stain unless you use simple orange or equivalent) that... well, it's gonna be dark
Every 500 miles? Please. My butt can't cash checks like that with 0w-40 M1 @ $6-7.5/qt.
Do NOT go over 6.4 quarts measured. Your Libby will eat it and you will add more wondering where the first cup went. Measure it, do not go by the dipstick. Measure your addition of 6.4 qts (oil filter empty) and notch your dipdtick if you have to. If you follow your dipstick (by ignoring my please to measure and pour), you will likely overfill it and blow even more sh:furious:t through it and the vicious cycle repeats itself.If your mechanic
does not know that the oil will be black with the pollution controls on, that should be a clue he should not be touching your diesel. 
Good luck, hope I don't come off too brash, I just don't want someone to take your money.
My
for you,Boilermaker2