I recently purchased a used grip for my RB67 from KEH in EX+ condition. It is the factory grip produced by Mamiya for the RB67. My concern is that the camera feels really heavy, especially with the CDS Prism Finder attatched. Will this grip hold up? Was it made for use with the RB while only using the waist level finder and small 90mm lens? The grip looks plastic. I am afraid it will snap in half when I least expect it. I would hate to damage my prism.