GE advantium SCA2001FSS

Question

My Advantium turntable rotates only intermittently. I suspect the motor or a partially broken ceramic square shaft that extends up from the motor at the bottom of the unit into the oven itself that the turntable assembly sits on. I've looked for a part schematic in order to identify parts that may need to be replaced with no luck. Any help here? It is a 220V 1100-1200 watt oven. Model no. SCA2001FSS 02

Thanks