Now goes out sailing with the old mariner (3,3)
I believe the answer is:
sea dog
'mariner' is the definition.
(synonyms)
'now goes out sailing with the old' is the wordplay.
I cannot really understand how this works, but
'now' could be 'ad' (AD, Anno Domini, as opposed to BC, Before Christ) and 'ad' is found within the answer.
an anagram of 'goes' is 'seog' which is located in the left over letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sea dog that I've seen before include "Old or experienced sailor" , "Experienced mariner" , "'Old salt (3,3)'" , "mythical creature" , "Ancient Mariner" .)