What type of mileage are you getting? What kind of car?

As far as the cloth return lines that stuff is very cheap from dealer. Get about 3 feet of it and do all the lines. After that use dawn dish washing detergent to wash engine down. It is cheap and works well to break down fuel and grease.

Follow fuel lines from tank to front the whole length. Look for dark spots, Especially around any clips that hold lines to the body.

Good Luck.

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86 300SDL. 250,xxx on #14 Head. One eye always on temp gauge.. Cruising towards 300K