When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Tape won't help if its leaking from o-rings, and if it leaking from the injector it could be a worn out copper washer, or not torqued enough(the book says to do 35 ft/lbs, but I did 45ft/lbs, 5 is a bit too low and will likely leak).
Is the flange on the injector line nice and rounded with no nics or gouges? Is the place where the injector line sits in nice and contoured for the injector line?
I'm not sure if the line can back up, I doubt it. Are you sure that the adapter if leaking and not the return line fitting right below? The o-rings on that injector could be leaking.