Possible Clues:

• Faithful servant
• Helpmate
• A chap giving essential help - that's me as crossword setter!
• Robinson Crusoe's assistant
• Sat after him with the crew, so it sounds
• Servant from Mayfair, North Dakota
• Sounds as if for the crew, so he always followed 8 down
• Fellow on island freed by a castaway, finally
• He worked by the day for the crew, so that's the way it sounds
• Reliable assistant father and I included in work unit