Paying a licensed plumber to do this work is probably worthwhile.

He knows what he's doing, he has the tools and parts to fix it to code and knows how to check it for leaks. When I had my gas line from the meter to the house replaced they got it done, had the inspector over to verify the leak check, and no it isn't soapy water, and did it all legal and proper in less than one day. Whomever had been working on your lines is obviously not qualified.

So if my house blows up due to a gas leak my insurance will have to pay and not be able to claim unlicensed repair.