Okay I think I found the vac line you're referring to, the one going to the center of the white round plastic thing atop the IP. I disconnected it but it's the original brown color so I can't tell by looking if there's oil in there. There's definitely oil ON the line...

The integrity of the line seems good as the shutoff lever functions as expected when running and when not.

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1987 300td 240k #14 head