Copper coil fittings leaking

Dear Kent, I have finally finished the installation of your DTX Cold weather SVO/WVO conversion kit and I have to say first and foremost that it is an incredible thing you have built. The instructions were thorough and easy to follow and the parts are so well designed. The kit essentially worked the first time I turned it on and has been working great since. (I will send u pics soon) The change over from Veggie to Diesel is nearly instant and I can immediately smell the difference each time I switch. I think it even runs quieter when I run on veggie oil. But the only issue I am having...and it is minor at that...is that the copper to brass fitting for the copper coil heat exchanger is leaking a little bit. I tightened both ends of the fittings but still there is some slight moisture dripping out. I am wondering if there is some trick to these fitting or if there is any special way I should tighten them?? Thanks again for all your help. -Drew