Been riding RM's for 10+ years now... they don't have the greatest clutches. We've found them to always drag somewhat, especially when bike is not running... even with good plates, springs, an aftermarket basket, and a good hub. Been running a thin automotive ATF (type f) for a while now, it helps a bunch. We keep just the minimum amount of freeplay in the lever too.
If you want to spend the big bucks, I've heard that Hinson's basket, hub, and pressure plate is a good fix... we've got their basket, it's a quality product, we just live with some drag.