The fuel supplied by French oil giant Total could be causing Red Bull's repeated problems with the mandatory fuel flow sensor in 2014.
It emerges that in qualifying in Shanghai, the reigning world champions struck trouble with the Gill-supplied device yet again.
To avoid a Melbourne-style disqualification, Red Bull reportedly adhered to an interim agreement reached with the governing FIA to revert to other measurements in the event of a sensor failure.
In the meantime, the search for the problem continues.
Speed Week correspondent Matthias Brunner has quoted the FIA's technical expert Fabrice Lom as explaining that the Total-supplied fuel is probably the culprit.
"On the sensor there is a seal that the chemical composition of the Total fuel could be damaging," Lom reportedly said.
"If this is happening, then the sensor would not work correctly."
Less clear, however, is why the Total fuel is damaging mainly Red Bull's sensors, rather than the ones used by the other three Renault-powered teams.
Meanwhile, it appears Red Bull is not ready to forgive rival Mercedes, after the German team called on the reigning world champions to be banned for three races for appealing Daniel Ricciardo's Melbourne disqualification.
Mercedes chairman Niki Lauda on Saturday made a peace-offering in the form of a Sachertorte, a famous recipe of Vienna chocolate cake.
But Red Bull's Dr Helmut Marko told Bild: "He thinks everything is over with a cake.
"I think the next time he wants to eat with us, he should put on a bulletproof vest."