Easy to change shaft, harder to pay for.
Yeah I’d try new after market lever. Make sure it clamps tight, if it needs some help then put it in a vice & run a hacksaw through the closed split to widen it & make it ‘bite’ more
Then clean spline, fit to best area & apply Loctite on spline itself. Worked on mine after a bit of fiddling to get the technique right.
If you have to replace the shaft spline then check out new price, but you could just find a 2nd hand one from a wrecker that is in good condition & is the same size or longer, then cut to size & weld (carefully) onto original RHS bit.