whats this part called?

its a welch plug. you put it in bulge out and smack it with a ball peen hammer to expand it. And yes, huge oil leak under pressure.
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ya it wasnt too oily in there, but every time i really got on it there was a trail of smoke, thought it was rear main seal! oh well had to pull engine anyways obviously!some people, you should see the bodywork and expanding foam insulation used to seal up wheelwells in trunk,aaarrrggghhhhhh!