The sealant used on the Fishers goes hard and cracks with age. You will need a very sharp craft knife/stanley and cut it all out. Replace with and marine sealant. To do this leave the sealant tube nozzle quite fine for the first run to get the sealand well inside between the teak capping rail and the hull. If water does penetrate it can find its way into the boat via the fastenings which hold the teak cap on.
Once initially sealed apply a much broader band of sealant. Then smooth off using the back of a spoon/teaspoon which you keep moist to avoid the sealant sticking and pulling.