Hi stuckinaffric, did you get to the bottom of your starting problems.
I am still having trouble with my Sedici. Glow plugs, alternator, starter motor, diesel injectors have all been replaced over the last year. On a cold start I have to leave the engine turning for 5 to 8 seconds now. Sometimes I have to stop it turning and try again. I have tested letting the glow plugs heat up, waiting for the light to go out, and repeat a few times, and then try and turn the engine over, with the same problem.
I'm not technical when it comes to car knowledge, but I am thinking it has to be something with the fuel line (I am guessing the pump is fine as I have no issues once the engine is running).
I've got to the point when I might well cut my losses and trade the car in next year, if it survives the winter!