Tom - The primary would = pre-filter on our 606's. You can just take the nut off, pull the fuel line and look down inside it and see if there is any particulate matter present and if so change both filters.

If you're concerned about gunk in the tank you could add some biocide or burn a tank of B99 if avail. If using either fro the first time you would want to have extra filters on hand in case the tank is gunked up and you clog a filter.

You should also look for a leaky o-ring again too.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)