03 7.3 aftermarket hpop lines?

So, my factory lines at 170k mi, were leaking at the seals. I thought, hey why not replace them? New lines came with fittings and a xover line, which I did not use or care to discuss, but after initial install began leaking at same fittings.
Now after 3 X r&r LEAKING!
Has anyone tried replacing these oversized, stiff, in the way lines with formed metal lines (like brake lines)?
Is there some reason this won't work?
If nothing else, how do I prevent the leaks on what I have now?
Please help me out here.