I replace my injector seals after (by accident) discovered that if you spray carburator cleaner around the injectors, the RPM's will vary, if they are leaking. Are you sure you did not wash the engine with water lately...?
Also, NAPA sells a inexpensive fluorescent die you can add to the coolant. Just poor it in, drive around for a while, check with a black light. Good luck!

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J.H.
'86 300E