Looks like filling in gaps is the definite way forward. I've got an ECO4 which is a factory modified Astra to increase fuel economy. I just had a look at the headlights and they have a rubber surround which looks like used to fill in gaps. I don't know whether it's an ECO4 specific mod, or standard on all Astras, but it's interesting to see this. It has the same rubber at the bottom of the headlights but it's hard to take a good picture of that.
