I disagree. Oily residue is flushed out using a detergent. Some have reported using Shout, Dawn, or any number of non-chlorinated, non-abrasive detergents as a flushant for oily residue. Citric acid flushes are designed to remove hard deposits, such as corrosion. We use citric acid in the lab to remove light rust from steel without attacking the base steel.

__________________
95 E320 Cabriolet, 169K