[spdbrake]

The Seco seals do work but are are usually are a last ditch effort to fix leaks.
Since they're dead soft annealed aluminum they cover for fitting and tube flaring defects. Going forward the Seco needs replaced every time the connection is opened.

Typically tightening the fitting and and loosening then tightening cures most leaks. Using Red or Green Scotchbrite and spin it on the flare with a suicide countersink helps a lot.