This is what I used when I reassemble the lights. Its factory sealant, also you take a spoon and push the original sealant back into the groves.. When you heat them up to reassemble the sealant get real pliable. Putting pressure on both sides of the light with mush them together. When the sealant cools off Bam, the lights are tight and sealed.
Only other thing that would allow moisture in is the access lid. If improperly put on it allows moisture in. Easy way to fix it is to open the access lid and blow dry the inside. Then put the lid on correctly. No need to take them off to do this, just undo some fender shroud pop out pins to get access to it.
Any way hope this helps..
OCI Butyl Rubber Glue - Accessories from The Retrofit Source Inc