I own a Pentax MX that I am cleaning up. I saw what looked like spider web around the prism. Removed the top cover, and upon removing the prism, discovered that the inside of the prism itself is cracked in a spider web manner. Question is, can I use the prism from an old Pentax MX that I have sitting around to replace the existing prism in the MX? Thought I would not bother to try if I am told it is not the same size & shape…….. Thanks in advance.