This has been a thing that really gives me the S**ts.

My partners 71 1200 does not have a fuel return or a little valve on the firewall that most late model datsuns have.

It leaks fuel out of the Fuel Cap, is this because the fuel cap ventilates and is incorrectly listed as the replacement for her car?

Should i just get a new one from nissan?

Go to the wreckers and get a second hand one from a 120Y.

It shouldn't ventilate from the cap. there is a ventilation system that vents out the floor after running through a bunch of clear plastic tube.

Cheers mate will do.

I also have the same problem I just fill it up half way now
will try the 120Y one too

the later ones don't vent, like the 120Y caps, the fuel system is made to vent through a carbon canister, but I'd expect to find the proper caps somewhere still.