Thanks for the post!

If you get oil in the line and through the air hose, most likely it is piston rings causing this. Most likely they're worn from excessive use and don't "wipe" the cylinder walls clean of oil like they should.

I would replace the Rings and go from there.

Also, make sure you install an inline Oil/Particulate Filter to catch the residual oil, as you'll most likely still get a small amount of oil in the line after you install new rings.

- MTR