What do the folks at MaxNC (now ximotion.com) say about it? Have you asked?
If you can't get G73 to work, try G83 (peck drill cycle). If you're using the MaxNC software, you might find that some of the more obscure g-codes like this aren't well implemented. Many MaxNC users have switched over to Mach3, which is more robust, works on more modern computers, and is better supported.
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