Please correct me if I am wrong on this but I beleive the later model 406 diesel was the HDi motor?

Else please be our guinea pig but if its an older type 2000 model then its mechanical injection and a whole lot safer, as far as I know. If its past 2002/2003 then its almost definately a HDi.

Owning a 307 HDi I would be strongly suggesting you go the bio route with the HDi engine. My main reason is the injectors, they are not the mechanical pintle type you have in older mechanical diesels at all, they are a piezo semiconducor type which injects 4 or 5 times per stoke. Yours will be quite similar I believe and if so you are lookign at $1000 approx per injector to replace minimum.

Regards,
Matt