While changing my spark plugs i found that they where all covered with oil ? chevy Aveo 2005

change them and wipe off oil then search for oil leak

Replace the valve cover gasket and spark plug tube O-r4ings

Yeah, kind of. The valve cover gasket needs replaced. The seals around the plugs go first because of heat. If the oil mark was near the top of the plug boot, replace the valve cover gaskets/seal. If it was near the bottom, slap in the plugs and wires.

Sounds like you may have a bad valve cover gasket. same thing was happening on my wife's Chevy Aveo. Valve cover gasket was worn and when I replaced it and cleaned plug wells, issue was resolved.As for the breather, I really wouldn't know why there's water in there.Only thing I would suggest there is to check your antifreeze level. Is it water from the antifreeze?

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Its possible that you need to take off the engine upper cover to check it.

Spark plug tube seals are leaking and need replaced along with the valve cover gasket. Any parts store should be able to get them for you. if left unrepaired it will eventually cause misfiring.

this sounds like the engine could have some bad valve guide seals allowing oil to be pumped into the combustion chamber of the engine, or you could have some broken pistion rings in the cylinders, i would get the vehichle checked out soon for this problem.

You have oil in the plug holes because the seals that are supposed to keep oil out are leaking-you need to remove the valve cover to replace them.

The valve cover has rubber o-ring seals that fit into the valve cover and seal oil out of the spark plug wells. Over time, they get hard and shrink, allowing oil to enter the plug wells from the top of the engine. You need to remove the valve cover and replace the valve cover gasket and o-ring seals. The seals should come with the valve cover gasket set.

Hope this helps,
Dave

try compression test and get back to me