You can reseal them yourself as long as you can get the tail light off. Just make sure you use something that doesn't harden like sikaflex. I used windscreen sealer. It's black sticky as hell, waterproof and never cures. A tube costs about $10. Easy job as long as you can get the light off.
Also, while you have the tailights off have a look at the external join of the seams that run down the back of the boot from the join at the guard. If they are cracked then they may be the culprit so use something to reseal them. I found mine were cracked so i cleaned out the original putty/seal and used some silicon...sounds a bit dodgy but it works