Have you by chance accidently set that floor brush as an entity? The leak looks like it is going through that.

It's a Func_Detail. Plus I've never had this problem before. I didn't really even change that part. (My friend who is great with maps did something to it to group together so I cant really just check the ONE block(carpet))
I just put a whole block around everything, leaks gone but still has me wondering.

It's because it's a func_detail, you can't use func_details to seal a map.

you must add a brush under the carpet with the invisible Texture tool, so it will seal the world
and if you friend has group the brush is surely for optimisation purpose of the map. and help VIS to compile more faster.

//red