Sounds to me you are using a oil that is not designed for 4 stroke motorcycle. There are lots of good brands out there with everybody having there favorite one. I have used Valvoline 20W50 4 stroke motorcycle in my R1 Yamaha with absolutely no clutch or engine trouble whatsoever.
Stock clutches are more than good enough for 1000 cc midget. Just remember plenty of free travel and use a motor oil that is designed for a 4 stroke motorcycle not car, truck or ATV and you will not have any trouble.
Bobby Layne