I think it's just the way the light shines. It appears to me to be one piece with the block, like maybe the factory was supposed to tap it and didn't because they use the port near the oil filter. I dunno. I know I'll get metal shavings, but I have to do something. I can always drain the oil after the operation. I get oil pouring out of there when I spin the priming tool by hand so I think that should get most of the shavings. Or I could shove a piece of rubber there to keep it from falling too far and then pump the oil up and it would push the rubber/plastic up?