NASCAR said they don't know what it is. They didn't say what it was or was not, because they don't know. At least that's what sources who know said around noon.
The "noted engine builder speaking confidentially" who said oil couldn't get into the intake was either a liar or a fool. All you have to do is have the intake gasket leak. Vacuum in the intake (and there is PLENTY of vacuum in a plate engine) will suck plenty of oil into the intake.
It was probably somebody working for Roush, since Roush has been crying about Toyota for years. Hell Roush has been crying about EVERYTHING for DECADES, back to when he was a crybaby in NHRA. Roush cried about Toyota spending money to buy wins, and then he went and offered Waltrip's employee (Larry Carter, crew chief for the 00 car) TRIPLE the salary to come to work for Roush, and got him to leave MWR.
Now, as to what the substance "could" be, there are any number of chemicals that add oxygen that "could" have been put in there. Plain old Sterno is one. The problem is, they took that manifold, allowed another manifold they inspected to be installed, allowed the car to qualify, and then immediately impounded the car, finding the same stuff in the manifold. So whatever was in there got in there from the engine running, and was not put in there before it was started. Besides, the 55 car wasn't even all that fast, although it would have qualified easily before the "top 35" rule. The 00 car from the same team was faster.