Same starting problems on a 2001 Scenic. Intermittent starting - fine one day, totally unreliable the next, culminating in it just not starting at all. It took ten minutes to take the sensor out, finding small metal filings on the sensor head. Wiping the sensor head clean did it. The car started straight away once reassembled. It is just a little awkward getting to the bolts on the 2001 Scenic.
Thanks very much for the tips - photos to help explain it were very accurate!!!