Update: just changing the clear filter didn't change anything. Dumped half a bottle of Diesel Kleen into the tank, seems to make a tiny bit of difference. Can't find the diesel version of StarTron for the life of me, and the marine places are closed for the holiday weekend so I can't try there. Bah. Clear filter is dirty again but at least is less black than the old one was. Have not changed the spin-on filter yet.

I'm reading about this trick where you add a bit of 2-stroke oil to the tank, but which kind to use?

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1983 240D, 272K+ miles (odo broke)