Resealing isn't horrible but you'll need some more glue. Headlight sealant is all that it's called. I've got lots of it but I'm going to need it here soon or I'd just send it to you. Anyway you'll need to cook the headlight in the oven at about 250 for 8 - 10 minutes depending on the appliance. Take a flat head screwdriver and pry the lens off of the headlight. From there you'll need to identify where your "leak" is and then clean up the inside really nicely. Then add your glue cold and then back into the oven for a heating session. Then the glue will be more pliable and should go back together flawlessly.
Since you're not doing any modification I'd say this takes an hour max per headlight. Just make sure you don't get the goo anywhere you don't want it. Acetone takes it off....but it also melts plastic.