The Dicor self leveling works pretty well. I bought a used 2007 TT last year and it also had a lot of what I would call hairline cracks around the vents, skylight etc. One or two were pretty open cracks, luckily no sign of leaking. I used Dicor SL liberally and it filled in nicely. I did re caulk one area later in the year. This spring I checked and it looks good although I did add a little Dicor just to be sure. Like the other poster said, clean the roof good and go for it.
I think ideally it would be good to remove all of the old caulk but mine was stuck pretty good, just cracked, and I did not remove it except in a couple of spots where it was not holding good.