Kallericcar

First off, my car has custom, pro-built twin turbo setup- 3.8 twin plug, TT, 700+ hp. Recently I removed the intercooler to replace the air filters and noticed the IC and piping was wet with oil. I cleaned and let the IC drain and reinstalled. The other day while idling at a slight incline in the driveway, oil smoke started coming out of the left pipe. With the muffler setup, it’s not obvious which turbo goes to which outlet. There is some oil seeping around a weld in the muffler from the left turbo.

Could this be the vent system, drains, or seals in turbos? I haven’t taken it out to drive it with some boost. How does vent system operate vacuum vs boost?