Mesh is part of the breather for the cam belt cover. the "hole" is where the wading plug goes in (for going through deep water)
IF engine oil is coming out, then your crank front seal is leaking. you'll need to strip the front cover and timing belt off, then pull the lower bet sprocket and then change the seal.
It'll pay to change the belt at the same time... the rubber can sometimes degrade when its covered in old oil.
Plus you'll need to clean out the whole area of old oil. Brake cleaner or petrol is good.