silicone might not be the best as a primary method of sealing. Did you try to through it into the oven and make sure the glue spreads on correctly?
Also, how did you apply the silicone? Where the 2 parts join, the crevice could be rather deep, if silicone isn't injected all the way in it could make the problem worst (wicking effect). I suggest you:
1) remove the headlight
2) Inspect for cracks or broken pieces
3) remove the silicone you put on
4) stick it in the oven at about 100C for 10 mins
5) push/spread the glue as much as you can
6) reseal with exterior silicone (all the way in) and all around.
If that still fails, get new headlights!
MODS: GMPP "Performance" cat-back, GMPP intake, GMPP extrude honed header, GMPP ground effects kit, lip spoiler, gen 4 headlights, DC sport strut tower brace, splitter, vortex generators, motegi SP10, Iridium spark plugs, ractive aluminum pedals, white carbon shift knob, shorty antenna, 4300K HID low beams (screw electricals warranty)