Seal with butyl first then silicone?
My process...
Remove all bulbs, screws, breathers etc
bake the lights in the oven... Preheated and turned off just before the lights go in. set a piece of cardboard on the oven rack and set the lights (1 at a time) on the cardboard...not directly on the oven rack.
Pull em open using welding gloves and a few flathead screwdrivers.
Clean out some of the old goop with screwdrivers
Pack the channel with butyl tape
Put back in preheated and turned off oven (let it come to temp first... Then shutoff before lights go in (on a piece of cardboard).
Pull em out, reinsert screws, clamp with a handful of clamps.
Redo the oven move with clamps on.
Take out while hot with welding gloves, press together by hand (with gloves) to insure good seating, recheck screws since the butyl has give still.
Let cool overnight.
Get 2 plastic grocery bags, GE silicone ii, caulk gun.
Make sure all bulbs and breather are removed still.
Prime silicone
Tear off a bit of grocery bag and wrap/cover your index and middle finger with doubled up pieces of grocery bag... Just a small portion to keep the silicone off ur fingers and the grocery bag strangely keeps the silicone from sticking to it, but after about 10min of contact u will have to throw away ur finger condom and make new 1 out of remaining grocery bag as the silicone deteriorates it.
Spread silicone onto the gap where the 2 halves of the light housing meets (do 1 headlight at a time here). Using your condomed fingers hold the housing of the light so the gap is facing up and the clear lens is facing towards your body (this way u can see the process). PRESS and work the silicone into the gap looking thru the clear lens side (remember?), Watch the silicone work into the gap and do this all the way around the housing. Maybe spread 6", of silicone at a time just so u can make sure ur getting good seal.
When done with each light, set lense side down onto a piece of cardboard and keep ALL bulbs and breathers OUT still. Let them set and off gas preferably 24hrs.
Then install hardware, put the lights in, go for a csrwash.
I've sent lights to Florida where they have been thru tons of mud, **** tons of humidity and rain, and not a single leak over years of abuse.
Maybe I take an extra step or 2, but I don't want to send out piss poor products.