That could have been one of my answers. I spent some time poking around the internet to see what the professionals use to clean injectors ultrasonically, and it was essentially a xylene-rich mixture. Other solvents were added (e.g., ethanol), but these other solvents didn't seem to be significant for cleaning.

Though xylene stinks like crazy, it seems to have much the same effect as mineral spirits, pentane, or heptane, all of which are relatively mild, non-polar solvents.

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95 E320 Cabriolet, 159K