I have one exactly the same on my 240. I like it because it has an 'O' ring type seal which does not leak and the cover can be removed many times withought having to buy gaskets. I took it off a car at Pic a Part.
From memory a Nissan Laurel.Not 100% sure on that though. I thought it was alloy, but turned out to be plastic.
i still have no idea and i need to get a gasket for it as it is not much use until i have one