Yeah the old oil is fine. I just ran out of my supply. I too bought a bunch of the Rotella.
I bought mine from here.
Zim's Autotechnik Brad Penn Oil - The Green Oil
I purchased 24 quarts of the 10w-30 and received it in 3 days. The first batch they sent me had the wrong viscosity and they next day aired out the correct oil and sent me a shipping label to return the other oil. Great customer service! The shipping was very reasonable at $15 and the package weighed 52 lbs.
That oil is packed full of the additives. You don't even have to run STP or Lucas with it..That sealed the deal for me because the additives in a bottle aren't cheap and the oil comes out to about the same price as the rotella.
Jason