First the year and model would be very helpful. I'll take a stab at it. That's not oil, just diesel fuel coming in contact with oil so it's dark like oil. Diesel fuel is a very good degreaser. There are crush washers at the base of the injectors but before pulling the injectors, replace the braided fuel hoses that run from each injector to another in series. It is very common for those to leak. If that doesn't fix it you'll have to pull the injectors and reokace the cruch washers but in the meantime you'll have to have the prechambers inspected as one could be cracked. That should keep you busy for awhile.

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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