I AM NOT a gas line expert, I'll admit. I will say that my parents lived in a house with LP gas for over 30 years, I was on LP gas for 14 years, I now know two men who work for a local LP gas supplier here for many years and have NEVER heard of an LP gas line needing cleaning. Now, if whomever told you this could share some creditability on having these lines cleaned, and share where this "oily" substance came from: I'm listening, so I can learn. The only gas lines I have ever had to clean was with a new installation running acetylene into an eight (8) bay service shop. ALL gas piping, both acetylene and oxygen piping had to be washed out three (3) time with 1,1,1, Trichloroethene, then the City inspector had to look into each pipe before we could use them. Wonder what he saw?