Leaky Tap (even after washer and seating tool)

[Eibbor]

I'm running out of patience with a leaky bathroom sink tap!

I changed the washer. But even after really tightening the tap would still be a heavy drip.

I then read about 'seating' so bought a tool. Did the grind, then replaced the washer again (as the old one got mangled and squished from me not attaching it properly and having to tighten it so much).

But it's still dripping?!

I'm not sure what else to try, any ideas?

[Eibbor]

I should add the current drip is very minor, but still very much a drip (and therefore an incomplete job and DIY fail).