The house I rented (before I was unable to work) had a nasty tub, which had been re-surfaced by a "pro" & had 3 spots where the new gunk flaked off, not to mention a few spots along the edge of the tub where mold had stained. It's not the most beautiful thing in the world, but I used some white caulk (an entire tube!) which is for use with vinyl siding--from the manufacturer of the siding, no less, as it comes in the exact colors to match their vinyl siding, and comes with a lifetime warranty like the siding. This might be similar to the most expensive tube of acryllic caulk one might find at a "lumberyard" or "home fixing-up products" type of place. I got it from the home improvement company where I worked at the time. I smeared it onto the spots, and all around the edge of the tub (& a few other spots on the walls) and then quickly & carefully smoothed it out because it dries rather fast, being acryllic/vinyl. I "sanded" it in a couple of spots with a nail file to make it even with the wall. The owner almost fainted when she saw the tub--she was delighted! The moldy spots have not been able to come through it yet, either. It is not shiny, though. One might fine a better & shinier method, that one just happened to be the cheapest within my reach--i.e., FREE!