Hi, Scott,
I have also situation with my Lambert, totally stuck. I heated, beat/vibrated, and forced. after all other petrolem and liquid chemicals, I had to cut open.
I used Dremel tool (TM) with very thin cutting disk (less than 1 mm.), and cut open a narrow and long slit without cutting into the stem. Then, jaw open the slot with thin and wide tool (say dull knife), some area I left paper thin metal but split open O.K.
I did not have any problem to put headset and locking nut after that, but if you wish, you can get someone (or yourself) weld the slot back closed.
I like to know how other members feel about this procedure.
Best regards,
KEN TODA, over the hill rider in North Carolina!