Must remember not to use second-hand fittings!

Tiling out the new bathroom and found this pipe fitting (a second-hand one) had a very, very small leak so shut off the water, stripped the fitting, put more PTFE sealing tape and retighten. Turned on the water and thought that would sort it. Didn't check immediately but when I did found that the leak was worse than before it had been touched! Turned off the water and left it until morning when a new fitting could be obtained.
Went to the plumbing merchant first thing the following day, removed the fitting which had been used previously and fitted the new fitting. 
Success! No leaks this time! 
It doesn't pay to use second-hand fittings even when that is all that is to hand at the moment!