I finally got around to installing the ambi safety and BCM extractor spring upgrade on my Bushy, and while I was at it I staked the castle nut and also drilled a drain hole in the bottom of the receiver extension. My question is, do you need to use the o ring that is included in the BCM kit? I tried to use it, but couldn't get the extractor pressed in far enough to insert the pin. And, is one drain hole enough on the bottom of the extension?, I see that the LMT ones have 3, I tried to drill a hole in the last 2 stops, but the one nearest to the back has solid metal above it, so I just drilled one in the next detent.