This is a typical problem with these rounded door showers used heavily in Fleetwood coaches. The rail forms an area that catches water in what I call “the moldy triangle”. When water sits in there, it will form scum, mildew, bacteria, and black mold.
This is my simple solution to fixing it.
two 1/8″ thick nylon spacers or washers. About the same size as a US dime.
Philips screw driver
Standard screw driver
Watch the video to see how simple this fix is and why it works.