Last night when I was kegging the big o-ring from the keg lid fell into my beer. It was sanatized so I'm not too worried but should it be ok in the beer?
then you will be just fine. don't sweat it as long as the first one was sanitized. and even if it wasnt a keg stored at keezer temps/serving temps will be too cold for any opportunistic infection to take off.
Same thing just happened to me while kegging up a Saison last week. I just grabbed a spare and sanitized it real fast. I think It was the Saison? We'll see soon enough.
I did this in my Maibock when I was kegging it about 2 months. At first mild panic set in then I just figured to let it be and see what would happen. We are about 1/2 way though the keg and have not noticed any problems with it. Just go to show: RDWHAHB/