One thing to check... I was fighting a distribution block leak (I thought). Tightened, loosened tighten again really tight and it still leaked. It turned out the leak was at the master connection. The fluid was travelling down the line and made it look like it was the block. Tightened the line at the master and all was well.

I did check that because something similar happened to me as well. One of the master lines goes into the top of this particular block. I had forgotten to tighten it at first, and everything was REALLY leaking.

Figured that out and thought I had it resolved, but unfortunately not.