blackish is poor as means burnt clutch pack ,reddy brown is normal colour of oil thats been in far too long,presume you mean lever feels right but you cant feel pull from box ,if thats the case it is possible lever/cable not exactly set you can test by holding pawl in lever in and moving lever a little forwards/backwards to see if that position engages better ,or clutch pack b or sticky valve ,clutch pack b could be repaired by competent diyer as only requires front on the box not a strip down