slavie

Don't get me wrong, I hope it works for you. If it stands the test of time, come back and post what you used, as leaky headlights seems to be a somewhat common thing on 957.
I'm just posting my experience with this never-ending saga. I used some industrial grade silicone, don't remember the brand (green tube), and applying it on the outside did not work. The area on the top side of the headlight has very thin gap between poly carbonate (or whatever it is) lens and black housing, and I think that's where it failed, because it came off easily there when months later I went to remove it and re-seal.

The headlight is exposed to engine bay temps on the inside, and gets really, really hot. There are no barriers or dividers, open tunnel to engine bay.

From factory, the sealant (I was not able to find out what Porsche uses on their headlights, but it is not the bytul rubber that all the other manufacturers use) is applied in the groove and seals the lens from 3 sides - outside, edge, inside. Like I said, I'm in the process this week of taking the lens completely off, cleaning out old sealant, and re-sealing it with black RTV that's rated for 500F. Other suggestions I've read are to use 3M Windshield Adhesive, but I've read enough folks stating they used RTV with great success (to re-seal lights, not just apply on the outside), so I'm just gonna go with that.