In my experience butyl tape is only used to bed/seal items that are being installed like windows, etc. Re-doing usually requires removal of the item, laying down new tape, and reinstalling.
I'd opt for caulk after removing as much butyl tape as possible. I have used plastic picnic knives int he past to scrape as much as possible out before caulking with a good urethane caulk.
Also, if you like black streaks, you'll LOVE butyl tape