For my daily driver, a black 1994 W124 E320 Coupe with 295500 km, I replaced a section of the brake pipe, between front and rear wheels, with copper pipe and intend to do the same with the gas pipes.
It was an interesting experience to do the brake pipe for the first time. In the attached photo the cut off steel pipe near the left rear wheel can be seen. It was connected with the new copper pipe using the same connection as the factory installed one near the front wheel (according to EPC).
It worked properly at the first attempt with no leaks or rejection by authority inspection (and still no leak after about 7 weeks).
I wonder if there are any disadvantages to using copper for the gas pipes?
1991 500E, 1994 E320 Coupe