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