Ed,

The black soot is o-ring wear which, in your case may have been accelerated
by other debris.  Sometimes, the initial wear occurs by cycling the gear dry
while everything is being fitted.  Another problem is that the fluid does not
flow "thru" this system -- that is, once filled the fluid just moves back and
forth in the cylinders and lines since the up and down side only meet in the
reservoir.  Of course, when you open the emergency valve, the two sides mix
differently.  There is a small quantity of fluid that never leaves the
cylinders - that amount at each cylinder end and this looks ugly when you
open up a cylinder since this is where most of the o-ring black residue
stays.   You are right -- you must keep everything clean and never re-use
fluid.

Scott Krueger