Replace the head, I have mixed experiences with T2 coil heads... one lasted like for a month!! other one only lasted for 3 days... the broken signs I have recollected from T2s are:
Less flavor, Less Vapor: Supposedly this is due a bad coil altough it also could be from a bad contact between the tank post and the coil head post, this happens on early stages of the atty like less than a week, I would say that this is a QA production issue.
Burnt Wicks: This normally happens after 2 or 3 weeks, it's the normal life cycle of the coil head but dry burning could accelerate the process, I realized that after you start getting a funky flavor, it's better to clean it up (no dry burn IMHO), if after cleaning and fill it the funky flavor still remains it's better to replace the coil head, the only way to fix the steady burnt flavor is rewicking and recoiling, is cheap and you can expect good results.
Dead Coil: Never happened to me on any Atty, I think this can only happens if you dry burn the coil hard, I learnt that Dry Burn is not good by any means (To clean is better to rinse and boil the heads or use edible alcohol, rinse with water and let it dry for a day).
For the leaking problem, I have experienced continous leaking when I overfill the tank or when I drag when the battery is off and sometimes when the battery is not fully charged. I would strongly suggest to do try this, clean the tank with warm running watter, remove the coil head, fill the tank with water just behind the 1.6 ml mark and dry the exterior of the tank with paper, leave it there for an hour or so and check if the tank is leaking ... if it leaks then now you will know that the leaking is due the tank (not the vaping behavior, or the liquid or whatever).