Crack above outside light - what to do about it?

When we bought our 2004 Lunar Clubman, it had a couple of little dents on the far side and also a faint crack above the outside light, about 6" long. We had the dents repaired and resprayed and the crack was filled and resprayed too. We have now noticed that the crack is reappearing - it looks like a line in the paintwork and like it will break through again at any time.

We presume it is movement and vibration that has caused the reoccurance and are unsure what to do now. As it isn't very noticeable we would just leave it but`are worried that water might get in and cause the dreaded rot and damp. Has anyone else had a similar problem and if so what did you do??