A 'black' fuel filter element can be indicative of having had microbial contamination or a significant amount of dead bodies from a contamination.. As for the rust colored; it is very likely corrosion. Welcome to our "separated water in diesel fuel club". All diesel fuel has some level of entrained water. Which is why John Kennedy and I use agressive emulsifying fuel additive, all the time. If not, one *will* experience exactly what you have: free water, rust/corrosion and a wonderful petri dish for microbes to flourish in. Some microbes can double in size in 20 minutes, given the right conditions: darkness, warmth, water and diesel fuel....
George Morrison, STLE CLS
George Morrison, STLE CLS<br />www.avlube.com e-mail avlube@netwalk.com<br />2002 Chev Duramax 2500HD, Delvac 1, Mobil 1 syn ATF, 75W-90<br />1998 Chev 3500HD 6.5TD, Delvac 1, Harvard 750S by-pass oil filter