The return lines generally need replacing anywho (they weep and then the biodiesel comes along and opens them up the rest of the way).

So whatever starts seeping is probably just an eariler indicator of a current problem. I put regular mercedes brand non-viton hoses on my return lines and just keep some spare on hand.
So far so good. The worst that it can do is eat up a few dollars in hoses over the course of few years.