The tiller Al tubing is an oddball size.
I sourced the closest possible I could find at my local specialist Al shop. It was slightly too big for the castings, so I had to machine the castings out enough to get it in.
I only did one initially (the broken one, naturally). It has held up well so far.
The other one let go a few years later, when I was about 2km off the coast of Torquay, out in Bass Strait. That could have been a bit exciting, except that it was my upwind rudder on a ~15km reach along the coastline, so I didn't really need it that day anyway 😄 .
Incidentally, if you ever get the chance to sail Torquay SC's Aus Day regatta, definitely do it. Torquay to Anglesea and back (if your boat holds together) in small cats. I plan to be there again next year.
I asked the Al shop to bend the tubing too but they didn't think it would bend without kinking. So I did my own bends too, using a long timber beam with the tiller tubing levered through a hole. About a dozen extremely slight kinks and the angle was perfect. Has held up well, as I said.