This is an example of an older fibreglass stair that had many cracks and bubbles on the top gel coat surface. All imperfections were prepped, repaired then the entire step was re-gel coated. As you can see there was quite a difference in the appearance of the before and after photos. This type of repair is easier to complete at the time of replacing the liner but could be completed at any time.
Watertown would be more than happy to come and give you a free estimate on any repairs that you might want resolved. Any cracks or faults in your coping can also be repaired in the same manor.