After you replace the shafts, you might look into having the splines touched up with a (horizontal) mill at a machine shop... as a kind of experiment/test for future 'beamers.
(If you were stateside, I'd ask for a shot at them...)
The twist happens on the end, where the splines engage, but they tend to prevent inserting the yoke past the point of twist. There is some fatigue/wear due to twisting, but if you extend and re-mill the splines from the free end towards the body of the trans, the yoke will at least slide up there again. Yes, it will be weaker. No, it won't be as good as before. But it should be serviceable for 'mature' street use for quite awhile.
This will only be prudent if the twist is very small, and visible to the casual observer only with a straightedge for reference. If it's offset by more than an eighth-spline, then it's probably done for. But if you had to look at it a couple of times to see what's going on, it could be 'saved', if not actually repaired.
If you have access to straight original parts, that's the best way to go. But 'trimming' the edges of the splines so things fit for assembly is inexpensive and worth a try. The fit/clearance of the part that's fully-engaged (at the very end, outboard of the twist) is the part that transmits the power via splines. The part not engaged does transmit torque too, but not via splines, but via the 'meat' of the shaft.
You'll probably want to go to an ag-repair shop for this, not a full-on CNC manufacturing place. My beat-up old Burke horizontal mill could do this quick and easy.
