Had a weird problem where a few times recently I've found found greasy snail trails of goo on the interior windshield under the sensors/rear view mirror. A clear sticky substance coming from behind the black cover where the cameras / sensors are top middle of windshield.

Turned out - the rain sensor had a problem or had melted (weird as it's not been hot or in the sun), it was replaced under warranty at my last dealer visit. I had noticed the rain sensing wipers worked intermittently / poorly (ie not sensing rain). This happened to me 15 years ago on an old BMW! Anyway kind of an odd one.