Hey guys I'm changing my knock sensors out on my 2000 Chevy Silverado Z71. Why am I seeing oil at the bottom of these holes? There's no Run marks down the walls the oil is just sitting in the bottom. Here's a link to a picture of it.
https://drive.google.com/file/d/14j4NeL6fs6Fbv3MjfZIOGy9MRjUYgZwT/view?usp=drivesdk

 

they seal the valley cover.

Just thread seal the replacements and you'll be fine. use oil resistant tape/sealer

 

ok thanks

 

You don't put anything on the knock sensors thread. That's a blind hole it does not go into anything. It's just an attachment point.

It's likely old oil that was spilled and run down there over time.