CLENZ-ALL
Poli Glow sells a product called Clenz-All. It is a cleaning paste that is non-toxic, biodegradable, non-caustic, phosphate free, and non-flammable. It is used to remove scum, algae, oil stains, chalking, yellowing, water-stains, black lines, tar, sap, bugs from fiberglass, etc. It can also be used in the galley and head.I recommend it to use on the marks you describe. It won't damage or remove the Poli Glow. I speak from experience.On a side note, I had inquired about becoming a distributor in my area for Poli Glow products since I have so many people at the boat yard asking me what I am using. I received a nice packet of information from Poli Glow. I have not acted on going ahead with this because of the investment in buying product to sell. If anybody is interested, you can go to their website and use it to send them a message of interest.