Yes
They are gaskets under your valve covers that keep oil from leaking out.
They both are under the valve covers, where the oil is slinging everywhere, when the motor is running. Perfectly normal.
There SHOULD only be oil inside the valve covers. If they leak coolant you have a serious problem.
Remove the oil breather cap on one of the valve covers and pour the oil through the hole in the valve cover.
The valve cover gasket is damaged. Needs to be replace.
It varies depending on the severity. if the damage isn't too bad, it could be piston rings, valve seals, pcv valve, and valve covers. in the worst case it could be a whole engine block, cylinder heads, cams, oil pump, oil pump pickup, valve covers, and pcv valve. generally ive been replacing the block, valve seals, valve covers, pcv valve, and oil pump.
adjust your lifters and valves under your valve covers to spec. look in your heyens manuel.
Well, if its motor oil you're talking about. You should see a cap on one of the valve covers (usually on the driverside valve cover). Take the cap off and pour in. The valve covers sit on cylinder heads. Hope this helps.
on the top of one of the valve covers is where it should be
only time you would need to replace valve covers,is if they are dented and allowing rockers to hit inside cover,or they have holes in em letting oil leak out. you may need to change valve cover gaskes as now and then they will leak oil
The oil return ports are located at each end of the heads near the short head bolts under the valve covers it's the hole at each end.
When you say "clatter" do you mean lifter/valve noise in the top end under the valve covers? Dirty oil will make the top end noisy because it is not lubricating enough to protect the components. Or the oil pickup is clogged. Best to change the oil if you know it is dirty and see how it sounds after that.