On most hypalon seam tape overlaps the glued connections between the chamber sections. The purpose is to protect the seam. Usually seam tape is thin and subject to abrasion so it wears/cracks/etc.
if the rest of the boat is fine i'd try and peel the seam tape back, remove any crusty glue and slightly abraid the surface below. Then use the inland marine liquid rubber. It is designed to adhere to hypalon, and can replace the seam tapes protective function
I've used it in this manner on seams before and it works great, but you will need heat or it will never cure. It takes awhile to cure even in 80 degree heat Dont even attempt it over the winter
Nice lines can be made using simple masking tape and you apply with the boat inflated. You may be able to get in colors other than black or gray
Hey, if you want me to take a dump in a box and mark it "guaranteed", I will. I got spare time.