did you disconnect the old slave cylinder at any time? If so, you just have air in the line. If you used the D series slave cylinder on the B and never disconnected it, it's gotta be caused by the leak you mentioned, or you kinked the line during the swap.

Just to let you know, the less other stuff you mention when asking for help (parts not related to the problem), the better. Reading through a page of "I had this problem but fixed it" just to get to the question you're asking is a pain in the poop shoot.

Anyway, congrats on the swap.