My 85' also leaks out that black sponge stuff.  I installed new springs, and the Orange high temp stuff.  It still slowly builds up black residue.  I just accepted it and didn't know my FMF on there could be oringed.  BUT THEN AGAIN, IM WAITING IN LINE FOR AN FTZ PIPE!  I can't wait till they start making them again.  

I'm thinking it could maybe be my power valve? I don't know, it doesn't seem to cause any problems.