When oil continues to drip or ooze after the burner shuts off, try replacing the standard nozzle adapter with a Delavan Adaptrap. The Adaptrap also helps eliminate erratic spray and flame flutter on burner shut-off due to air in the oil line.
Any time you experience air in the oil line it is a good idea to check for leaks especially around fittings and valves. Use a clean cloth or paper towel to dab under each fitting to detect any oil present. Tighten or replace any leaky components.