You should not need that seal and I would recommend removing it all together if you are using the Nukatap Taps.
The only reason to use that seal is if you are using a tap that was not purchased from KegLand and the tap is not well designed.
As you can see from this diagram here:
https://kegland.com.au/cdn/shop/files/Nukatap_KL15509_6a03bcc1-7fe0-41db-8175-91ad69d5c0ee.pdf
The tap should seal on the shank sealing washer (seal number 9).
This is the most sanitary place to seal so beer doesn't end up around the knurling.
It's only for poorly designed taps and shanks that you should seal on the face of the tap body.
So when I use the normal seals with the Klock quick connects (male onto the tap) and a return spring you can't get them tight enough to seal and beer comes out the side
So normal washer and no spring you
I can get full collar engagement
With Spring I can't get the collar to fully engage so it won't seal on the washer and it leaks
In saying that I find the spring feels like it's binding if I overtighten and doesn't feel as smooth as one I've got on a balllock disconnect currently
Edit:
Went and checked my other tap
I set this one up after I'd done the Klock so went straight to a shank seal instead of the washer
Note the latest ball lock adapter fits the spring better (not as tight) reassembled with a washer and no leaks etc (collar fully engaged)
Klock tap swapped onto the old style balllock adaptor also no issue with the washer
I've got a ballock male to shank and triclamp to tap shank adaprers as well but can't be bothered testing that right now
The K Lok has no teeth to engage the tap either
The spring seems alittle big for the Klok hole and doesnt slide in as easy as the other two fittings
Springs seem to be 17.5mm diameter (not the most accurate measuring) and the Klok hole seems to be 17.1mm I can force the spring in the hole but its not as easy as the other two
Latest adapter is 18mm ID
Old adapter is 18mm but is does taper down to 13mm at the bottom
Is this an issue you have with stock at site?