It seems many are opting for the wet system for the troublesome 300 starter, as it requires much less maintenance & generally just works better. It involves cleaning/removing all the old waxy grease that KTM uses, sealing up the sidecover weep hole, shimming the starter correctly(as previously mentioned), some folks add a breather tube/hose vent to the electrical grommet, then adding a few ounces of oil for lubrication. I personally use Red Line Synthetic gear oil as the crown wheel/starter shaft spline is basically a differential, and the synthetic gear oil works well & remains fairly thin, even though it is an 85w/90 oil. Red Line synthetic gear oil, awesome stuff as anyone who has used it knows. I have modified the plastic cover so that can be easily removed to access the crown wheel so I can add a couple ounces of oil every month or so, as it does seep/weep oil a bit. At the end of the season take it apart and it's clean as a whistle in there. No wear, no corrosion, much less hassle than taking it apart every month to relube. It is also necessary to get a decent battery(7series or Turn Tech). The only issue is the fact that I can only get 1 season out of a set of brushes. My bet is that KTM changes the design soon as other 2 strokes spool up with a more troublefree estate system. Do your brush sets come with a new brushholder? and are the bushings available for the sidecover separately?

Where can i purchase new needle bearing and oil seal for my starter motor?

the newly available bushing for the side cover/case/bendix shaft is 55140030100.

The bevel gear, or intermediate shaft coupling as KTM call it, also uses this bushing, and they can easily drop out when reassembling the case if you’re not careful. There are 4 in total.

I understand that you can get the shaft bushing & seal. Google "KTM starter parts" and check Rick. He may have them.