I went ahead and change the small piece of 4mm fuel tube from the fuel in brass tube to the T festo, this small piece of tubing with time shrinks and if it is disturbed like I did when I replaced the starter O ring the the seal will break and it will start leaking, changing it will solve the small fuel leak, there is no other place under the engine's front cover that I know of where fuel could leak.

The fuel leak is so small that it didn't show when I was running the engine at home, it only came to be visual after the 7 minutes maiden flight.

I will report my findings after I fly the Roo again