Hubby has fitted new taps in wash basin, had to use brass extenders from Bunnings to give extra height. Cannot get a leafless seal! We have tried PTFE and fix a leak blue PTFE to no avail. The leak is occurring between the spindle of the new tap and the extender. Any ideas what else we could try? We have screwed up as tight as we ca go - and that's tight!

Is this the eitting in question? Let me know, Tom