That Navajo is a great boat. Campways were almost the only alternative to Avon for good quality "back in the day." I suspect that the hypalon layer on your seam tape is all that is worn down, and the underlying seams are OK. It is hypalon, so go with something compatible, not PVC. I might mention that I've found TearAid to be an unbelievably good product, and am wondering if strips of that would work? I used some TearAid on a ducky puncture a few years ago and it is still holding strong. I also put it over the labels in my PFD's to keep them from losing their ink or tearing before the jacket itself is actually worn out. (I've been on at least one river where the rule is/was that if the label cannot be read or is torn up, the jacket is no good). If you can find a boat repair shop, and if the boat is otherwise worth the investment, letting a pro do it makes sense. Otherwise, follow glue instructions "to the letter" and use a heat gun to cure it up, etc. Seam tape can be time-consuming to put on. That's why the TearAid approach (it just self-glues) has some appeal. Remember there are two kinds of TearAid, Type A and Type B. Don't recall which is which but one is for hypalon, neoprene, rubber, etc. and the other is for PVC, urethene, etc. Get the right one if you try it. Would be interested to know how it works out. Buena suerte.