Just replaced the original thermostat on my 1.4 Stilo. Used a Vernet (French) equivalent but discovered it leaked at the gasket because the edges of the bolt holes on the engine side of the housing sat proud of the flange. Therefore it was not possible to tighten the whole flange against the gasket. Belatedly looked at the original part and found it was perfectly flat around the bolt holes. My advice is to use the Fiat part for this job.