I'm afraid this is something that is caused by the age of the strake. On my old Broom it was a constant source of annoyance and in the end I just replaced the lot.
Try the "Back to Black" type trims aerosols from your local motor accessory shops. The Draco one looked dreadful and marked everything badly, this stuff seems to seal the rubber and deffo made it better. Note it took 2-3 apps before it finally looked good, but that didn't matter 'cos SWMBO was doing it.....