I replaced mine one month ago. https://www.ducatiforum.co.uk/threads/solved-hyper821-big-big-problem.74217/page-2 I had the same thought... aftermarket or OEM...just the sprag or the complete kit? NO DOUBT OEM and all the parts (sprag, main gear and flange). You need the generator cover removal tool, flywheel lock tool, threadlocker to the thread of the crankshaft and the nut, dynamometric wrench to tighten the cranckshaft nut and some patience. I suggest to replace the cranckshaft nut. Its not an expensive part. Another point is be carefull to separate the flange and the sprag from the flywheel. It is supposed to be done inserting two screws from the flywheel rotor-side in their holes in order to remove the flange. I fucked the screws thread and had to order new screws. Just use another screws.