Is that what the black grease was? Crank seal leaking?

 

Possible,could have been there from assy if it was really just grease,but the only way to tell for sure was to have done a leak down or to just have replaced the crank seal since you were already there.. Seals take as much wear as pistons,rings,etc and best to replace them anytime you do a top end,stators or even when puling clutches off since you're there. Easier than having to go back in later if seals are in question.