Door seal leak

I have a small leakage of rainwater (yes it does occasionally rain in Scotland) from the top of the driver's door. The door seal looks to be fine. I wonder if there is any magic gunge I can get from Halfords to smear onto the seal to help?
The door looks to be flush with the bodywork when closed so I don't think the locks need adjusted, but I am no expert.
Howard

You could try smearing vaseline over it, or if the leaks bad you could cut a bike inner-tube in half and glue that to your seal with a puncture repair kit