Remove all the old caulking/sealant - scrape it all away and clean the surface well. Re caulk it (heavily...at this point it's not about looks but function) - make sure it's done it warm or hot weather it give it a chance to cure and make sure it's a good outdoor and UV resistant. Then use a spray leak seal (clear or colored) over top of the caulk. If it still leaks the vent it cracked or faulty or you have a tear/hole in the roof itself. Good luck.
Flextape! Not sure how or why but I saw an infomercial on it yesterday. Sounds a lot like the eternabond stuff.
Is Justin Competent, or just incompetent?