Hey Stu, the one way clutch is by far the most common problem with the otherwise very dependable Nippon Denso starters. Harley sells a repair kit for $113 MSRP, P/N 31516-94, that includes some extra parts most folks don't need, or you can do like I did and buy just the clutch from one of the many places on ebay selling Harley starter clutches. I spent $45 including shipping for just the clutch, and it's been working better than the original. There are some places hawking supposed lifetime warrantied replacements for a lot more money, but IMHO what you're paying all that extra for isn't really a better clutch, the higher price is what makes the "free" warranty replacements possible.
The actual replacement isn't all that difficult, but on the '06 and earlier models you do have to remove the outer primary in order to remove the starter from the bike (to remove the jackshaft bolt). If you don't have a manual or previous experience taking a starter assembly apart, you can find exploded view drawings online. These starters are also used on Toyota's and other automobiles, btw.
Jerry