I see the nailing flange and there is mildew in the gap which I have tried to clean out. There was a musty smell coming from the tub/shower unit and I think that is where it came from. Would really like to prevent a re-occurence. Your advice please?
Also-if your advice is to caulk it, there is some lime/water mineral deposit build up on the fiberglass. How do you get that off? OR do you even need to remove it if we caulk it?

Are you talking about your bicycle or your car?

I see the nailing flange and there is mildew in the gap
What's a "nailing flange" and a gap between what? More details please, Tom