Possible Clues:

• Do they make 'er, perhaps, happy in many ways once a year?
• One is happy to get many of them on one's birthday
• It's enough to make you mad to 1 across things
• Happy to have a birthday when one gets back
• What you expect to get back if you go back to the South
• Might this be what happens to `er for profit?
• Perhaps it's 'er that makes them profitable
• Profits from soaks' drinking vessel
• Word in many a sequel title
• Much I.R.S. mail