Comparison between a virgin Quicksilver water separating gas filter , and a used Sierra equivalent, in service for 2 years. The Mercruiser / Quicksilver is part 35-866340K01 and the Sierra is a popular line of marine replacement parts. The Sierra was in service for about 100 hours, or about 1200-1500 gallons of gas. The reason I post this here is because they are almost identical to oil filters. Some observations - Sierra does not seem to have any coating on the inside, while the Merc has a claimed epoxy coating. Very important considering that water builds up in the filter. - Merc internal coating had air bubbles under the paint, and the end-plate was not coated on the inside. So good idea, poor execution on the internal coating. - Sierra external coating was not as good as Merc, and had noticeable rust spots. - Sierra not apparently coated on the inside, but I did not detect any internal rust. There was a tiny bit of water present when I drained the filter into a jar. - Sierra has more filter area, Merc has more water holding capacity. - Sierra had an assembly defect- the black nitrile gasket was offset and probably did not seal 100%, which might let dirty fuel bypass the filter. - Sierra made in Taiwan, Merc in US. - Merc / QS always on left, Sierra on right if 2 pics are side by side. Honestly I was disappointed by both of them, but I would give the Merc a 6 out of 10, and the Sierra a 4 out of 10. I might consider a Racor for such an important part.