I have not installed a Mac version, since nobody is responding to this, I would do the dumpprivkey and then importprivkey:
launch your bitcoin client as usual and wait for it to load the blockchain and start up
click on ‘help’ in the menu bar (top right)
click on 'debug window’
select the ‘console’ tab
type: walletpassphrase “your walletpassphrase here” 600
type: dumpprivkey [your public key here]
this will return the private key, you can copy it now; ensure you clear your clipboard/history afterwards
type: walletlock
and in your linux client:
click on ‘help’ in the menu bar (top right)
click on 'debug window’
select the ‘console’ tab
type: walletpassphrase “your walletpassphrase here” 600
type: importprivkey thatverylongprivatekey