Sad to hear that the 300V did not work for you. I was thinking of going from Agip Extra HTS 5w40 to Motul 300V 10w40.
Do you have any reviews on Mobil 1 Supersyn 5w50? My 156 usually consume 0.5L of oil per 5,000km. But with the Mobil 1 Supersyn 5w50, the engine consumed 0.5L in 2,000km...