Banker occasionally sorry adding international name above old firm (7)
I believe the answer is:
orinoco
'banker' is the definition.
(I've seen this before)
'international name above old firm' is the wordplay.
'international name' becomes 'orin' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'above' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'firm' becomes 'co' (a firm is a company).
'orin'+'o'+'co'='ORINOCO'
'occasionally sorry adding' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for orinoco that I've seen before include "moves between South American banks" , "may be seen running through South America" , "South-American river" , "large flow of water" , "Colombia/Venezuela river" .)