Your tiller looks as if it was the wrong wood to start with.
Teak is the obvious first choice but virtually unavailable. Iroko is the usual strong substitute and generally available from timber merchants. Any carpenter/joiner or DIYer who can use a plane and sandpaper can shape a replacement from the pattern of your broken tiller.
I made a new tiller for my superseal, and other boats before, it's not difficult.
Philip
The rascal, superseal