I took the liberty of merging the two related threads on the same topic.
The photo that was taken of the drive area of the bike in question is so microscopically small that I can't see anything meaningful.
Number one thing to check is if the center nut on the pulley is tight. If it's loose as was shown in the video (of someone else's bike - we think) then it may have the same issue: The splines in the pulley are shot, probably because the pulley was not clamped properly because someone didn't tighten the center nut properly. If that's the case then the fix is the same: replace the pulley and this time tighten the center nut properly. The bent washer that the video points out is bent because that bent-over edge helps to retain the nut from loosening ... it isn't something wrong, it's supposed to be bent (and you have to bend it when installing the nut. If you don't, the nut will come loose. That bent-over edge is the only reason the center nut in the video didn't come off leading to the pulley in the video coming completely off the shaft.)
The second thing to check is whether the belt is good. I can't tell in the microscopic photo that was provided. If the teeth are all intact and it looks like the shape of the teeth meshes with the sprocket well and the edges of the pulley aren't chewed up (indicative of misalignment) then the belt technically might be OK although belts have both a "mileage" limit (that you are probably not past) and an "age" limit (that you probably ARE past). It's the same technology as timing belts in car engines.
Replacing that belt looks like a bear of a job. It's not like a chain that can be split and put back together with a master link. The whole belt is one piece. That means the swingarm has to come off so that you can get the belt around the swingarm pivot. That means you need to suspend the bike in some way so that the weight of it is off the rear suspension. It might have a center stand ... that will do.
Expect this to be a few hours of labour in addition to the cost of the parts.
Now, as for that belt ...
There is a fair chance that it uses an industry standard tooth pitch and width that is called "HTD" or a variation of it that I will describe below.
https://www.torontogear.com/powerhouse-htd-belts/ Make some measurements.
Belts are available off the shelf in specified numbers of teeth. Count yours and compare to what's in that catalog. If it is an off the shelf belt (including tooth count) then you are all set. If it is an oddball then you are stuck buying the OEM Kawasaki belt.
Now - Important - Look for some manufacturer's markings on the belt. It would have originally been printed on the outside. If the manufacturer is Gates, then it is probably not an HTD belt, but a very similar one that is called Gates Poly Chain GT. For more info ...
https://www.gates.com/resources/res...oly-chain-gt-carbon-belt-drive-systems-manual
If it is an HTD belt, you need the strongest and most durable one you can find ... not the cheapest. If it is a Gates Poly Chain GT, it already is. Do not mix up HTD and Poly Chain GT ... the belts and sprockets are similar (to the point of being hard to see the difference unless you can see manufacturer's markings) but not identical.
I had a service call years back because our company's purchasing department had a policy of taking whatever part number engineering specified and looking for the cheapest alternative. In the case of a timing belt drive on a rather expensive machine, where engineering specified a high-quality belt and purchasing substituted a cheap one, that didn't work out too well. I spotted the problem the moment I took the cover off. Don't cheap out on this part.
N.B. Judging by the way this final drive is designed, it might be possible to retrofit a chain drive. If someone has done it before, there's probably info on the internet for how to do it.
