I just changed the fuel filters in my Yanmar 2GM20F. The Raycor filter had a slight layer of black gook in the bottom of the plastic bowl screwed on the bottom. Nothing appears to be floating in the fuel itself. And the secondary filter looked clean in the bowl. It's been just over a year since the last time I changed the filter. Am I looking at a bad fuel tank?? Is there a such thing as cleaning a fuel tank? The motor works perfect and always starts and runs so pretty sure it's not made it into the injectors.
As always any suggestions greatly appreciated.