I have this issue with oil leaking from the backside of the engine block on top. It’s a 2.2L Ecotec engine. There is some type of rubber cap just diagonally to the right of the oil filter cap. It had quite a bit of oil gather in it. Can someone let me know what this is? I have searched high and low for the name of it. I have included a picture with a yellow line pointing to it, and a yellow outline. Thanks in advance!