Wow... guy asks for help with a leak and he denounced and told to use air. Seriously. ..wtf... not helpful and seems to be a rash of that lately.
The proper answer should have been to 1) point to the watercooling sticky and make sure you read it thoroughly, 2] inquire if you used compression or barb fittings and how it is secured, 3) how did you tighten the fitting into the block, 4) and if your ends were cut straight and clean
Glad to hear you found a solution, and sorry no valuable advice was given. So what did you discover anyway?