Do the blanks on the extra radiator ports have o-rings installed also?
Well, in you pic you're using the res port #3 which requires an extender which is included in the res packet if you buy it new, I quote again:
"IMPORTANT NOTES:
1. When using ports #3, #4 or #6 it is mandatory to use the enclosed EK-Extender G1/4 (EAN: 3831109845165) due the ports being recessed into the plastic
Reservoir Bottom."
EDIT Kaku beat me to it
I can't link:
YOUR BASKET
1 x EK Water Blocks EK-CSQ Extender 8mm G1/4 - Black Nickel £1.99
Total : £4.27 (includes shipping : £1.90).
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That APPEARS to be it
the one included is
Item no:::::::3831109845165(If you google this, the exact fitting should be on OEM site)
linked one is: 3831109845974