Fuel filter effeciency

[cad58y]

1986 300SDL in CC storage for the last 10 years. Recently got it running without much trouble. Changed all fluids and replaced primary and secondary fuel filters. Drove it about 15 miles and noticed that the inline filter contained a large amount of sludge/sediment (looks like rust). My question is how effective are the filters in protecting the fuel injection system from damage. I plan to drop the tank and have it coated but am concerned that i may have already caused damage. Thanks, Bob Smits