Thanks for the post!

When air compressors push oil into the air tank and lines/tools, this is usually due to defective Rings.

I would take the Head and Cylinder off of the pump and look at the Rings; do the gaps line up (they shouldn't)? Are the rings stuck inside the Piston grooves so that they're flush with the Piston (they shouldn't be)?

Unfortunately if you do need the Rings, they're no longer available from the manufacturer (DeVilbiss). The original Ring Kit part# is KK-4313, maybe you can still find an outlet online that still has the kit in stock.

Also, make sure you're running the right kind of oil in the pump, you want straight 30 weight NON-detergent oil in there. I know this seems obvious, but you'd be surprised.

Most likely you'll find that the Rings need to be replaced, but also check the small metal Reed Valves that are screwed onto the Valve Plate (right underneath the Head). Make sure these Valves aren't rusty or damaged.

- MTR