I just removed a quail with the same problem from my '29. I wrapped it around the base of the cap with soft leather and used a large pipe wrench. I gently turned it first as if I was tightening it; then again very gently applied pressure as to loosen it. It came off with no problems. Someone (not me) had put it on with some kind of locktite sealer.
Quail cap for sale, with thermometer, good condition, need set screw: $40 plus shipping.