With two days of pre-season testing remaining, the reigning world champions took a heavily revised car to Barcelona recently and guarded the rear exhaust solution intensely, with covers and - oddly - even umbrellas.
Initial analysis indicated it might be close to what the FIA will allow, following the strict clampdown on exhaust diffuser blowing.
Asked by the Kleine Zeitung newspaper if the FIA has completely banned the aerodynamic use of exhaust gases, Marko replied: "No.
"The regulations stipulate the position of the exhaust, within a certain parameter."
As for the 'cheating' rumours, the team advisor insists: "It bounces off us completely. The way we see it, there are no grey areas and we are well within all the regulations."
Meanwhile, FIA technical delegate Charlie Whiting has admitted it is "quite likely" he will have to "revisit" the exhaust regulations for 2013.