Had a go at fixing mine last week. My symptoms were a little different in that the starter had sounded like it was struggling a bit for a while, like it was low on volts, but the battery had plenty of juice & the connections to the starter looked good. Then it started just whizzing when the button was pushed & not turning over the motor at all. I got the NZ$9 SKF seal as above & took it apart.
The 3-arm flywheel puller we had did not even look like shifting the flywheel, even with a few good whacks. The local KTM dealer didn't have the right flywheel puller
but there was one in the country so $49 & a day later I was the proud owner of the genuine factory service tool which did pop it off nicely.
The spring did indeed look buggered, everything else looked OK so I put it back together with the new spring which seemed to fit well.
Once the rest of the bike was back together I tried the starter & it worked, but it still sounded like it was struggling, & after about 6 starts went back to just whizzing & not working at all
I don't really mind that the cheap fix didn't work, it was worth a shot, but now I'm not sure if I need a whole new sprag clutch assembly, if the inner or outer hubs it engages on are worn, or if the starter motor or solenoid are worn out & the starter not spinning quickly enough is messing up the sprag clutch somehow???
In the meantime my kick-starting technique will no doubt continue to improve