SMR Tap Bush 30mm 3409R
If you can remove the existing valve without removing the Valve brass bush then you might not require this valve brass bush spare part, or if the leak stops just by replacing the Cartridge, then you can return the Valve Brass bush for a refund.
Below is the 3409R bush on the two threaded valve (shown here the 3984R with blue seal, and the 1212R valve with white seal would look same other than it has a white seal underneath).
And here is the one threaded 3819R valve version of the two threaded 3984R / 1212R below :
And for illustrative purposes, here below is the same one threaded 3819R valve with the wider bush 3409R (bush c.36mm diameter)
This same Bush 3409R is also used on other valves as well , depending on the Tap. Again see the difference between the wider 3408R Bush (36mm) and the smaller 3409R Bush (30mm)