Well, I did the tool for the pinion anyway. I found a fitting in the plumbing box which looked good.

To get the geometry right, I did an epoxy cast of the grooved nut:

Epoxy cast

I used a hack saw guided by the epoxy and took the rough part with an angle grinder:

In the rough

The final part was done with a file:

Finished tool

The fit is pretty perfect actually..

Regards,
Karsten