Thanks Guys... I think I was getting a little too lost in the detail of the workshop manual which shows complete clutch removal, requiring a locking jig. I can see now that's it's purely a matter of draining the oil, removing the clutch cover/springs/plates, then replacing everything with new.
Yeah, the ELF HTX 740 oil does seem to come highly recommended, but with some using other brands of light gear oil and others ATF, there's no definitive solution. Reading through the myriad information available on the 315r and it's clutch issue(s), tends to suggest that replacement of the stock steel clutch plates fitted to early MY 315's with aftermarket (dimpled) ones, or those from an appropriate MY CR250, in combination with using light gear oil and correct clutch adjustment, should do the trick.
Fingers-crossed.
Thanks again.