Got any pictures of the "gunk" ?

Curious as to what it is... What kind of filters are you running the fuel through prior to putting it in the car?

Sounds like you got a process down that works, but if the oil changed you may not realize without doing a titration on it. The 3/27 is only a "guess", you can't really rely on it for conversion % unfortunately. Recently this has come up and it's turned out to not be as accurate as people thought. Having 1.5ml drop out doesn't mean 50% conversion.

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'98 E300 Turbo "Juliette"
'85 Federal 300TD