Grizzy,
There have been loads of threads discussing the various types of alternative to Rotoflexes ever since this forum started- now far too many threads to make much sense of the subject?
If I could attempt to give an overview of what has been written:
Modern H&S regulations have resulted in Rotoflexes (and all other rubber components in the suspension and drive-train) being inferior to original spec, service life is MASSIVELY reduced, cost has MASSIVELY increased.
Spydersport produce a shaft with Rotoflex at one end and CV joint at the other; this means twice as much distortion of the remaining Rotoflex; not a good idea with modern rubber.
Tony Thompson produced sliding-spline shafts intended for racers with reduced suspension travel; these can be modified by grinding, or suspension droop can be limited; some of the methods used were designed by Heath Robinson but it can be done.
Mick (Susan) Miller (and others in the USA and Australia) produced CV shafts intended for road use, they work very well but require the heavy-duty diff mounts (top and bottom) to counteract the increased shock-loading due to removal of Rotoflex "sponginess". Tony Thompson is the best source for these in the UK. Susan had some quality-control problems and stopped supplying the shafts a while back- I'm not sure what the current position is, unfortunately.
If you trawl through the numerous threads it is noticeable that more than a few contributors adopt a rather defensive position on whatever type of shafts they currently have fitted to their cars; however, there is most definitely a trend for those who have changed from Rotoflexes to CVs to say that they would not go back. That is the camp I'm in.
Somewhere in this thread
lotus-gearbox-f37/solid-driveshafts-they-improve-the-driving-experience-t16269.html you will find a photo I uploaded showing what happens to new standard Lotocones in a matter of months, if you go for CVs; with the TT indestructible part shown alongside.
If you want to come over to Wilmslow and stick your head under two Elans with Miller shafts, drop me a PM.