That's your wastegate, you can bolt a turndown pipe there if you can fit one.
That oil leak is not good, spray it down with some brake parts cleaner to clean it up. Next time you run the engine, check to see where the "fresh" oil is coming out of.
The lack of an o2 sensor might be whats causing it to stall. Is it using the stock computer? It should be mounted above the glovebox under the dash.
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