That's weird indeed... No leakage anywhere? It only has a seal at either end of the housing and an o-ring between the 2 halves if i'm not mistaking... You did use proper gearoil last time you changed it of course? Maybe as Johnny says something came in through the venthole but only thing ever to do that was water on mine during a period of heavy rain causing the oil to come out grey and misty, not black and sticky... Keep us informed if you find out!
