Shouldn't Full flow mods be using 3/8" NPT? the stock bypass setup is 1/8"...
What size lines? compression fittings or? Is it possible you have the lines over-constrained and too much motor flex?
If it's so hard to see etc, how do you know for sure that its leaking where the fitting screws into the block?
Pipe threads with a little RTV shouldn't be leaking...
A picture of how you have everything routed would be helpful...
