In many of the boats I see the vinyl is pretty well shot.  Age and exposure to sun and heat will eventually dry out and cause the vinyl to fail.

If you have a cut or tear in your vinyl and the vinyl is still good it is repairable, mold and mildew on vinyl that is still good is re dyeable . If you have splits running through panels or seam separations, you are better off replacing. In many older boats there are issues with rot and decay in the wood seat bases and backing boards of trim.

If you have someone work on the vinyl of your boat please insist they use Stainless Steel staples ( difference in cost of steel and stainless staples is substantial) .  You will not notice the difference now, but you will in a few years. I also use sewing thread  designed to stand up to sun and chemicals ( the last solar lux thread I purchased was 175.00 a pound).  Use someone who has the ability and willingness to replace rotted wood parts and doesn’t just cover them up.