weeping rear brake lines

Was the rear brake hose re-used when the new stainless lines were installed? Brass is soft and the "seat" where the line seals can get crushed from the original lines. Then when you go and change lines(that had a good mating ) they no longer seal perfectly. Stainless can be a rascal to deal with. I do most of the brake line jobs at our shop( to date I've used 381 25 foot rolls of copper/nickle/iron(called cupro) brake line and 128 25 foot rolls of steel. I'm not bragging-just stating my experience.
I've done more than a few stainless kits and by far the best sealing material is the cupro stuff. If changing the hose doesn"t help or it"s already been changed maybe try the cupro stuff-it flares well,is easy to bend and will never rust out. It polishes up nicely too! I hope my blabbering helps......