The left engine mount holds all the torque of the engine. The standard part is a fluid filled mount that is prone to splitting. When it splits you get a thud from the engine, often when turning (left hand I think).
 

I sent my split mount to RES (Rotary Engine Specialists) in Auckland, who got a local crowd to burn out the rubber and replace it with urethane. The result is a solid mount that passes a little more of the rotary energy pulse to the seat of your pants. Nice.
 

I chose not to replace the right hand mount, as there was no need.