Coolant Dropping Audi A6 C7

Hello,

i have had my car pressure checked and extensive testing with the coolant system but all hold pressure etc. i had taken it to a specialist in my area and he said when the under cover was removed there was still no sign of leaking coolant. however he did see some moisture near the 'V' so could be a crack in the V but needs to taken apart to see. he also said its not bad enough to be worth paying so much for a strip down as they still may not find anything obvious there. 

any ideas what to do next? i am thinking to buy extended warranty as this sounds like i am about to be hit with an extensive bill. which warranty would you guys also recommend? 

thanks in advance

Manz