Had that problem. Even the "easy out" wasn't easy, would not loosen the old vent. Of course, once I ended up w/ a hole that big I had to take it out, so used a series of progressively larger drills until I go to a point where I though the orignal threads were. Picked out the liner remains w/ a steel scribe for a turn or so (far as I could get) to expose the start of the barrel threads, then "retapped" it to remove the rest of the liner. Gotta be very cautious you don't drill into the threads on the barrel.