Since this collar is no longer available, try wrapping the bottom threads of your burner with Teflon plumbers' tape. This will seal the gap between the burner threads and the lamp/s glass threads, and will allow you to gently unscrew the burner to add fuel without damage. Every few years replace the tape, or as it becomes worn.
#2 size BRASS INSERT collar
Note the angled scalloping around the lamp's glass neck's rim.