the additional $10 is for TNB analysis, that measures how much of the additives remain the oil. This is vital info if you are pushing the oil beyond what is "normal" for your vehicle and oil (they call that extended drain intervals). Just replacing filters along the duration will keep soot under control (unless you have lots of blowby) but a lack of additives makes for increased engine wear.
I am right around 5500 miles and decided 1 year is long enough to remain in the car (thats only 5500 miles in one year on my '87 300D turbo)
I just sent a sample off to Blackstone, after making up a topsider using a small magnetically driven pump. I learned you have to keep a sharp eye on the jug the oil is bing pumped into, in my case an old 1 gal Delo jug. I went to get the Blackstone jar for the sample. They advise against taking the first oil that comes out nor the last oil that comes out of the engine. Anyhow, I raced back and was about to switch off the pump and the first jug already started overflowing and I had a little oil on the ground
Remember the Valdeze
