Shucks, don't worry about it -- stress in everyday life is a beautiful thing for all of us. What does not kill me, makes me grumpy.
For most things but especially things used as tools, IMHO if it works, it's fairly clean, and the operation is not impaired, it'll do "as is." So, if the stuff on the inside of the light isn't going to drive you crazy, it's no big deal. Where it comes from is probably one of lifes little mysteries, but if it won't hurt the light and cleaning it out will be more work than it's worth, it will become one of those funny little stories you'll laugh about in a few weeks.
Don't get me wrong. I like to have things as perfect as I can get 'em, but I also know when to leave the tools alone. Mostly what happens is that I have a tool or a light that I have just spent several hours getting into pristine condition, and the first use for it will be around something like molybdenum disulfide grease, aka moly grease -- you know, the stuff that you get the one, single drop on you that will cover every clean thing in the house, if not the planet -- anyone who has been there will tell you. It's my interpretation of the Law of Dimishing Returns meets Murphy.