I clean parts ultrasonically in solvent every day. It's never blown up in my face. It's rather alarmist to say to NEVER use solvent. The caveat is to not let the ultrasonic run too long, or the solvent will overheat and may cause a fire. Anything under 30 minutes is safe. Anything longer than that either needs to either be attended to, or the bath needs to run on a timer.

Many injector cleaning houses use xylene as solvent.

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95 E320 Cabriolet, 159K